Updating a local tree for a client synchronization service

ABSTRACT

The disclosed technology relates to a system configured to detect a delete event for a content item at a first location on a local file system of a client device, wherein the first location on the file system is managed by a content management service. The system determines a second location for the content item and whether the delete event is associated with an add event for the content item based on the second location of the content item. If the delete event is associated with the add event, the system processes the delete event with the add event in a unitary update to a local tree, wherein the local tree represents a file system state.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/858,146, filed on Dec. 29, 2017, entitled, UPDATING A LOCAL TREE FORA CLIENT SYNCHRONIZATION SERVICE, which claims the benefit of priorityunder U.S.C. § 119(e) to U.S. provisional application No. 62/611,473,filed on Dec. 28, 2017, entitled, SYNCHRONIZED CONTENT MANAGEMENTSYSTEM, all of which are hereby expressly incorporated herein byreference in their entireties.

BACKGROUND

Content management systems allow users to access and manage contentitems across multiple devices using a network. Some content managementsystems may allow users to share content items and provide additionalfeatures that aid users in collaborating using the content items.Content management systems generally store content items on servers andallow users access to the content items over a network. Some contentmanagement systems also allow for local copies to be stored on a clientdevice in order to provide users with faster access to content items ina more natural interface (e.g., a native application or within the filesystem of the client device). Additionally, this allows the user to haveaccess to the content items when the user is offline. Content managementsystems attempt to synchronize copies of a content item across a numberof client devices and the servers so that each copy is identical.However, synchronization of content items is difficult and is associatedwith numerous technical obstacles.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-recited and other advantages and features of the presenttechnology will become apparent by reference to specific implementationsillustrated in the appended drawings. A person of ordinary skill in theart will understand that these drawings only show some examples of thepresent technology and would not limit the scope of the presenttechnology to these examples. Furthermore, the skilled artisan willappreciate the principles of the present technology as described andexplained with additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1 shows an example of a content management system and clientdevices, in accordance with some embodiments;

FIG. 2 shows an example of a client synchronization service, inaccordance with some embodiments;

FIG. 3 shows an example of tree data structures, in accordance withvarious embodiments;

FIG. 4 shows an example of tree data structures, in accordance withvarious embodiments;

FIG. 5 shows an example method for synchronizing a server state and afile system state using tree data structures, in accordance with variousembodiments of the subject technology;

FIG. 6 shows an example method for resolving conflicts whensynchronizing a server state and a file system state using tree datastructures, in accordance with various embodiments of the subjecttechnology;

FIG. 7 shows an example of tree data structures illustrating a violationof a rule for an add operation, in accordance with various embodiments;

FIG. 8 shows an example method for incrementally converging a serverstate and a file system state, in accordance with various embodiments ofthe subject technology;

FIG. 9 shows an example of tree data structures, in accordance withvarious embodiments;

FIG. 10 shows an example scenario;

FIG. 11 shows an example Venn diagram representation of two plans ofoperations, in accordance with various embodiments of the subjecttechnology.

FIG. 12 shows an example method for managing changes in plans ofoperations, in accordance with various embodiments of the subjecttechnology;

FIG. 13 shows an example scenario, in accordance with variousembodiments of the subject technology;

FIG. 14 shows an example method for updating a local tree, in accordancewith various embodiments of the subject technology;

FIG. 15 shows an example method for updating a local tree in response toa move or rename operation, in accordance with various embodiments ofthe subject technology; and

FIG. 16 shows an example of a system for implementing certain aspects ofthe present technology.

DETAILED DESCRIPTION

Various examples of the present technology are discussed in detailbelow. While specific implementations are discussed, it should beunderstood that this is done for illustration purposes only. A personskilled in the relevant art will recognize that other components andconfigurations may be used without parting from the spirit and scope ofthe present technology.

Various advances in computing and networking technologies have enabledcontent management systems to provide users with access to content itemsacross multiple devices. The content items may include, but are notlimited to, files, documents, messages (e.g., email messages or textmessages), media files (e.g., photos, videos, and audio files) folderscontaining multiple files, or any other unit of content. Content itemsmay be shared with multiple users, edited, deleted, added, renamed, ormoved. However, synchronizing these content items across severalcomputing devices (e.g., servers and client devices) and across severaluser accounts has remained flawed and rife with technological obstacles.

To illustrate some of the technical obstacles, a first machine (e.g., aclient device or server) may send communications to a second machinethat provide information about how a user has modified content itemsmanaged by the content management system. These communications may beused by the second machine to synchronize the content items on thesecond machine such that actions performed on content items on the firstmachine are reflected in content items the second machine and thecontent items on the first machine are substantially identical to thecontent items on the second machine.

However, there may be several communications sent and the communicationsmay be received out of order as a result of various network routingprotocols used by the one or more networks used to transmit thecommunications, the technical operations of the first or second machine,or some other reason. Furthermore, a user may be performing a largenumber of modifications to a large number of content items, undoprevious modifications in a short amount of time, or quickly performadditional modifications to a previously modified content item or set ofcontent items. This increases the likelihood that these communicationsare received out of order, certain communications are out of date, orthat the second machine will perform operations on content items thatare not up to date. As a result, many of the operations may not becompatible with the current state of the content items. In fact, it maybe difficult to even detect whether some operations are in conflict withother operations or with the current state of the content items.

Additionally, there is an inherent latency with respect tosynchronization actions. For example, actions taken on the first machineis first detected by the first machine, and a communication is generatedand then transmitted through a network. The communication is received bythe second machine which may still be processing previouscommunications, processed, and actions detailed in the communicationsmay be taken at the second machine. In this illustrative scenario, thereare several points where latency is introduced by limited computingresources (e.g., bandwidth, memory, processing time, processing cycles,etc.) of the first machine, the second machine, and the network. Aslatency increases the likelihood that communications, for some reason,conflict with the current state of the content items are increased.Furthermore, processing these conflicted communications and resolvingthe conflicts also expends needless computing resources such asprocessing time, memory, energy, or bandwidth and further increaseslatency.

To further complicate matters, the same or different user on the secondmachine and/or additional machines with access to the content items mayalso be performing modification to the content items. As a result, theissues above may be multiplied and additional technical issues arise asto whether local actions conflict with remote actions and/or whetherlocal actions are operating on up to date content items.

The disclosed technology addresses the need in the art for a clientsynchronization service for a content management system that provides atechnical solution to the technical problems above as well as others.The client synchronization service may be configured to operate on aclient device and identify synchronization mismatches between contentitems on a server of the content management system and correspondingcontent items on the client device. For each synchronization mismatch,the client synchronization service may identify operations needed tosynchronize the content items and initiate those operations.

The client synchronization service may track the status of content itemson the server, the status of content items on the client device, andtheir synchronization state using a set of tree data structures(“trees”). According to some embodiments, a set of 3 trees may be used.The three trees may include a remote tree that represents a serverstate, a local tree that represents the file system state on the clientdevice, and a sync tree that represents a merge base for the local treeand the remote tree. The merge base may be thought of as a commonancestor of the local tree and the remote tree or a last known syncedstate between the local tree and the remote tree. Accordingly, theclient synchronization service may determine that the server state andthe client device state are synchronized when all 3 trees (e.g., theremote tree, the sync tree, and the local tree) are identical.

When a modification to the server state of the content items or theclient device file system state (“file system state”) of the contentitems is detected, the client synchronization service updates theappropriate tree and determines whether the server state and the filesystem state are synchronized based on the triumvirate of trees. Basedon the update to one of the trees, the server state and the file systemstate may become synchronized, become unsynchronized, or become furtherunsynchronized. If the server state and the file system state are notsynchronized, the client synchronization service may identify at leastan initial set of operations needed to converge the server state and thefile system state and get the server state and the file system statecloser to a synchronized state.

By relying on the set of tree data structures to monitor the serverstate and the file system state provides alternatives and/or solutionsrooted in computing technology to various technical problems. Forexample, the client synchronization service is able to track the serverstate as well as the file state and store a representation of a mergebase of the two states. As a result, the various embodiments of thesubject technology avoid the technical problems associated withreceiving a number of communications specifying how users are modifyingcontent items remotely and determining which order these modificationsshould be implemented locally, whether the modifications conflict withother modifications or are out of date, and whether remote modificationsconflict with local modifications performed locally by users. Many ofthese issues arise from other solutions not being able to track thestate of the various actors involved (e.g., the server and the clientdevice) and not being able to quickly determine whether the states arein sync. Instead, these other solutions rely on receiving instructionson how to modify content items locally, without the context of whetherthe server state and file system state are in sync.

Furthermore, since the server state and the file system state arecontinuously monitored, determining whether they are synced is much moreefficient in terms of procedural complexity as well as computing timeand resources. As is described in further detail below, the clientsynchronization service enables the incremental and methodicalsynchronization of the server state and the file system state in a moredeterministic manner. As a result, the scaling and testing of contentmanagement system features is also more efficient.

Content Management System

In some embodiments, the disclosed technology is deployed in the contextof a content management system having content item synchronizationcapabilities and collaboration features, among others. An example systemconfiguration 100 is shown in FIG. 1A, which depicts content managementsystem 110 interacting with client device 150.

Accounts

Content management system 110 can store content items in associationwith accounts, as well as perform a variety of content item managementtasks, such as retrieve, modify, browse, and/or share the contentitem(s). Furthermore, content management system 110 can enable anaccount to access content item(s) from multiple client devices.

Content management system 110 supports a plurality of accounts. Anentity (user, group of users, team, company, etc.) can create an accountwith content management system, and account details can be stored inaccount database 140. Account database 140 can store profile informationfor registered entities. In some cases, profile information forregistered entities includes a username and/or email address. Accountdatabase 140 can include account management information, such as accounttype (e.g. various tiers of free or paid accounts), storage spaceallocated, storage space used, client devices 150 having a registeredcontent management client application 152 resident thereon, securitysettings, personal configuration settings, etc.

Account database 140 can store groups of accounts associated with anentity. Groups can have permissions based on group policies and/oraccess control lists, and members of the groups can inherit thepermissions. For example, a marketing group can have access to one setof content items while an engineering group can have access to anotherset of content items. An administrator group can modify groups, modifyuser accounts, etc.

Content Item Storage

A feature of content management system 110 is the storage of contentitems, which can be stored in content storage 142. Content items can beany digital data such as documents, collaboration content items, textfiles, audio files, image files, video files, webpages, executablefiles, binary files, etc. A content item can also include collections orother mechanisms for grouping content items together with differentbehaviors, such as folders, zip files, playlists, albums, etc. Acollection can refer to a folder, or a plurality of content items thatare related or grouped by a common attribute. In some embodiments,content storage 142 is combined with other types of storage or databasesto handle specific functions. Content storage 142 can store contentitems, while metadata regarding the content items can be stored inmetadata database 146. Likewise, data regarding where a content item isstored in content storage 142 can be stored in content directory 144.Additionally, data regarding changes, access, etc. can be stored inserver file journal 148. Each of the various storages/databases such ascontent storage 142, content directory 144, server file journal 148, andmetadata database 146 can be comprised of more than one such storage ordatabase and can be distributed over many devices and locations. Otherconfigurations are also possible. For example, data from content storage142, content directory 144, server file journal 148, and/or metadatadatabase 146 may be combined into one or more content storages ordatabases or further segmented into additional content storages ordatabases. Thus, content management system 110 may include more or lessstorages and/or databases than shown in FIG. 1.

In some embodiments, content storage 142 is associated with at least onecontent storage service 116, which includes software or other processorexecutable instructions for managing the storage of content itemsincluding, but not limited to, receiving content items for storage,preparing content items for storage, selecting a storage location forthe content item, retrieving content items from storage, etc. In someembodiments, content storage service 116 can divide a content item intosmaller chunks for storage at content storage 142. The location of eachchunk making up a content item can be recorded in content directory 144.Content directory 144 can include a content entry for each content itemstored in content storage 142. The content entry can be associated witha unique ID, which identifies a content item.

In some embodiments, the unique ID, which identifies a content item incontent directory 144, can be derived from a deterministic hashfunction. This method of deriving a unique ID for a content item canensure that content item duplicates are recognized as such since thedeterministic hash function will output the same identifier for everycopy of the same content item, but will output a different identifierfor a different content item. Using this methodology, content storageservice 116 can output a unique ID for each content item.

Content storage service 116 can also designate or record a content pathfor a content item in metadata database 146. The content path caninclude the name of the content item and/or folder hierarchy associatedwith the content item. For example, the content path can include afolder or path of folders in which the content item is stored in a localfile system on a client device. While content items are stored incontent storage 142 in blocks and may not be stored under a tree likedirectory structure, such directory structure is a comfortablenavigation structure for users. Content storage service 116 can defineor record a content path for a content item wherein the “root” node of adirectory structure can be a namespace for each account. Within thenamespace can be a directory structure defined by a user of an accountand/or content storage service 116. Metadata database 146 can store thecontent path for each content item as part of a content entry.

In some embodiments the namespace can include additional namespacesnested in the directory structure as if they are stored within the rootnode. This can occur when an account has access to a shared collection.Shared collections can be assigned their own namespace within contentmanagement system 110. While some shared collections are actually a rootnode for the shared collection, they are located subordinate to theaccount namespace in the directory structure, and can appear as a folderwithin a folder for the account. As addressed above, the directorystructure is merely a comfortable navigation structure for users, butdoes not correlate to storage locations of content items in contentstorage 142.

While the directory structure in which an account views content itemsdoes not correlate to storage locations at content management system110, the directory structure can correlate to storage locations onclient device 150 depending on the file system used by client device150.

As addressed above, a content entry in content directory 144 can alsoinclude the location of each chunk making up a content item. Morespecifically, the content entry can include content pointers thatidentify the location in content storage 142 of the chunks that make upthe content item.

In addition to a content path and content pointer, a content entry incontent directory 144 can also include a user account identifier thatidentifies the user account that has access to the content item and/or agroup identifier that identifies a group with access to the content itemand/or a namespace to which the content entry belongs.

Content storage service 116 can decrease the amount of storage spacerequired by identifying duplicate content items or duplicate blocks thatmake up a content item or versions of a content item. Instead of storingmultiple copies, content storage 142 can store a single copy of thecontent item or block of the content item and content directory 144 caninclude a pointer or other mechanism to link the duplicates to thesingle copy.

Content storage service 116 can also store metadata describing contentitems, content item types, folders, file path, and/or the relationshipof content items to various accounts, collections, or groups in metadatadatabase 146, in association with the unique ID of the content item.

Content storage service 116 can also store a log of data regardingchanges, access, etc. in server file journal 148. Server file journal148 can include the unique ID of the content item and a description ofthe change or access action along with a time stamp or version numberand any other relevant data. Server file journal 148 can also includepointers to blocks affected by the change or content item access.Content storage service can provide the ability to undo operations, byusing a content item version control that tracks changes to contentitems, different versions of content items (including diverging versiontrees), and a change history that can be acquired from the server filejournal 148.

Content Item Synchronization

Another feature of content management system 110 is synchronization ofcontent items with at least one client device 150. Client device(s) cantake different forms and have different capabilities. For example,client device 150 ₁ is a computing device having a local file systemaccessible by multiple applications resident thereon. Client device 150₂ is a computing device wherein content items are only accessible to aspecific application or by permission given by the specific application,and the content items are typically stored either in an applicationspecific space or in the cloud. Client device 150 ₃ is any client deviceaccessing content management system 110 via a web browser and accessingcontent items via a web interface. While example client devices 150 ₁,150 ₂, and 150 ₃ are depicted in form factors such as a laptop, mobiledevice, or web browser, it should be understood that the descriptionsthereof are not limited to devices of these example form factors. Forexample a mobile device such as client 150 ₂ might have a local filesystem accessible by multiple applications resident thereon, or client150 ₂ might access content management system 110 via a web browser. Assuch, the form factor should not be considered limiting when consideringclient 150's capabilities. One or more functions described herein withrespect to client device 150 may or may not be available on every clientdevice depending on the specific capabilities of the device—the fileaccess model being one such capability.

In many embodiments, client devices are associated with an account ofcontent management system 110, but in some embodiments client devicescan access content using shared links and do not require an account.

As noted above, some client devices can access content management system110 using a web browser. However, client devices can also access contentmanagement system 110 using client application 152 stored and running onclient device 150. Client application 152 can include a clientsynchronization service 156.

Client synchronization service 156 can be in communication with serversynchronization service 112 to synchronize changes to content itemsbetween client device 150 and content management system 110.

Client device 150 can synchronize content with content management system110 via client synchronization service 156. The synchronization can beplatform agnostic. That is, content can be synchronized across multipleclient devices of varying type, capabilities, operating systems, etc.Client synchronization service 156 can synchronize any changes (new,deleted, modified, copied, or moved content items) to content items in adesignated location of a file system of client device 150.

Content items can be synchronized from client device 150 to contentmanagement system 110, and vice versa. In embodiments whereinsynchronization is from client device 150 to content management system110, a user can manipulate content items directly from the file systemof client device 150, while client synchronization service 156 canmonitor directory on client device 150 for changes to files within themonitored folders.

When client synchronization service 156 detects a write, move, copy, ordelete of content in a directory that it monitors, clientsynchronization service 156 can synchronize the changes to contentmanagement system service 116. In some embodiments, clientsynchronization service 156 can perform some functions of contentmanagement system service 116 including functions addressed above suchas dividing the content item into blocks, hashing the content item togenerate a unique identifier, etc. Client synchronization service 156can index content within client storage index 164 and save the result instorage index 164. Indexing can include storing paths plus a uniqueserver identifier, and a unique client identifier for each content item.In some embodiments, client synchronization service 156 learns theunique server identifier from server synchronization service 112, andlearns the unique client identifier from the operating system of clientdevice 150.

Client synchronization service 156 can use storage index 164 tofacilitate the synchronization of at least a portion of the contentwithin client storage with content associated with a user account oncontent management system 110. For example, client synchronizationservice 156 can compare storage index 164 with content management system110 and detect differences between content on client storage and contentassociated with a user account on content management system 110. Clientsynchronization service 156 can then attempt to reconcile differences byuploading, downloading, modifying, and deleting content on clientstorage as appropriate. Content storage service 116 can store thechanged or new block for the content item and update server file journal148, metadata database 146, content directory 144, content storage 142,account database 140, etc. as appropriate.

When synchronizing from content management system 110 to client device150, a mount, modification, addition, deletion, move of a content itemrecorded in server file journal 148 can trigger a notification to besent to client device 150 using notification service 117. When clientdevice 150 is informed of the change a request changes listed in serverfile journal 148 since the last synchronization point known to theclient device. When client device 150 determines that it is out ofsynchronization with content management system 110, clientsynchronization service 156 requests content item blocks including thechanges, and updates its local copy of the changed content items.

In some embodiments, storage index 164 stores tree data structureswherein one tree reflects the latest representation of a directoryaccording to server synchronization service 112, while another treereflects the latest representation of the directory according to clientsynchronization service 156. Client synchronization service can work toensure that the tree structures match by requesting data from serversynchronization service 112 or committing changes on client device 150to content management system 110.

Sometimes client device 150 might not have a network connectionavailable. In this scenario, client synchronization service 156 canmonitor the linked collection for content item changes and queue thosechanges for later synchronization to content management system 110 whena network connection is available. Similarly, a user can manually start,stop, pause, or resume synchronization with content management system110.

Client synchronization service 156 can synchronize all contentassociated with a particular user account on content management system110. Alternatively, client synchronization service 156 can selectivelysynchronize a portion of the content of the total content associatedwith the particular user account on content management system 110.Selectively synchronizing only a portion of the content can preservespace on client device 150 and save bandwidth.

In some embodiments, client synchronization service 156 selectivelystores a portion of the content associated with the particular useraccount and stores placeholder content items in client storage for theremainder portion of the content. For example, client synchronizationservice 156 can store a placeholder content item that has the samefilename, path, extension, metadata, of its respective complete contentitem on content management system 110, but lacking the data of thecomplete content item. The placeholder content item can be a few bytesor less in size while the respective complete content item might besignificantly larger. After client device 150 attempts to access thecontent item, client synchronization service 156 can retrieve the dataof the content item from content management system 110 and provide thecomplete content item to accessing client device 150. This approach canprovide significant space and bandwidth savings while still providingfull access to a user's content on content management system 110.

Collaboration Features

Another feature of content management system 110 is to facilitatecollaboration between users. Collaboration features include content itemsharing, commenting on content items, co-working on content items,instant messaging, providing presence and seen state informationregarding content items, etc.

Sharing

Content management system 110 can manage sharing content via sharingservice 128. Sharing content by providing a link to the content caninclude making the content item accessible from any computing device innetwork communication with content management system 110. However, insome embodiments a link can be associated with access restrictionsenforced by content management system 110 and access control list 145.Sharing content can also include linking content using sharing service128 to share content within content management system 110 with at leastone additional user account (in addition to the original user accountassociated with the content item) so that each user account has accessto the content item. The additional user account can gain access to thecontent by accepting the content, which will then be accessible througheither web interface service 124 or directly from within the directorystructure associated with their account on client device 150. Thesharing can be performed in a platform agnostic manner. That is, thecontent can be shared across multiple client devices 150 of varyingtype, capabilities, operating systems, etc. The content can also beshared across varying types of user accounts.

To share a content item within content management system 110 sharingservice 128 can add a user account identifier or multiple user accountidentifiers to a content entry in access control list database 145associated with the content item, thus granting the added user accountaccess to the content item. Sharing service 128 can also remove useraccount identifiers from a content entry to restrict a user account'saccess to the content item. Sharing service 128 can record content itemidentifiers, user account identifiers given access to a content item,and access levels in access control list database 145. For example, insome embodiments, user account identifiers associated with a singlecontent entry can specify different permissions for respective useraccount identifiers with respect to the associated content item.

To share content items outside of content management system 110, sharingservice 128 can generate a custom network address, such as a uniformresource locator (URL), which allows any web browser to access thecontent item or collection in content management system 110 without anyauthentication. To accomplish this, sharing service 128 can includecontent identification data in the generated URL, which can later beused to properly identify and return the requested content item. Forexample, sharing service 128 can include the account identifier and thecontent path or a content item identifying code in the generated URL.Upon selection of the URL, the content identification data included inthe URL can be transmitted to content management system 110, which canuse the received content identification data to identify the appropriatecontent item and return the content item.

In addition to generating the URL, sharing service 128 can also beconfigured to record in access control list database 145 that a URL tothe content item has been created. In some embodiments, the contententry associated with a content item can include a URL flag indicatingwhether a URL to the content item has been created. For example, the URLflag can be a Boolean value initially set to 0 or false to indicate thata URL to the content item has not been created. Sharing service 128 canchange the value of the flag to 1 or true after generating a URL to thecontent item.

In some embodiments, sharing service 128 can associate a set ofpermissions to a URL for a content item. For example, if a user attemptsto access the content item via the URL, sharing service 128 can providea limited set of permissions for the content item. Examples of limitedpermissions include restrictions that the user cannot download thecontent item, save the content item, copy the content item, modify thecontent item, etc. In some embodiments, limited permissions includerestrictions that only permit a content item to be accessed from with aspecified domain, i.e., from within a corporate network domain, or byaccounts associated with a specified domain, e.g., accounts associatedwith a company account (e.g., @acme.com).

In some embodiments, sharing service 128 can also be configured todeactivate a generated URL. For example, each content entry can alsoinclude a URL active flag indicating whether the content should bereturned in response to a request from the generated URL. For example,sharing service 128 can only return a content item requested by agenerated link if the URL active flag is set to 1 or true. Thus, accessto a content item for which a URL has been generated can be easilyrestricted by changing the value of the URL active flag. This allows auser to restrict access to the shared content item without having tomove the content item or delete the generated URL. Likewise, sharingservice 128 can reactivate the URL by again changing the value of theURL active flag to 1 or true. A user can thus easily restore access tothe content item without the need to generate a new URL.

In some embodiments, content management system 110 can designate a URLfor uploading a content item. For example, a first user with a useraccount can request such a URL, provide the URL to a contributing userand the contributing user can upload a content item to the first user'suser account using the URL.

Team Service

In some embodiments content management system 110 includes team service130. Team service 130 can provide functionality for creating andmanaging defined teams of user accounts. Teams can be created for acompany, with sub-teams (e.g., business units, or project teams, etc.),and user accounts assigned to teams and sub-teams, or teams can becreated for any defined group of user accounts. Team's service 130 canprovide a common shared space for the team, private user accountfolders, and access limited shared folders. Team's service can alsoprovide a management interface for an administrator to managecollections and content items within team, and can manage user accountsthat are associated with the team.

Authorization Service

In some embodiments, content management system 110 includesauthorization service 132. Authorization service 132 ensures that a useraccount attempting to access a namespace has appropriate rights toaccess the namespace. Authorization service 132 can receive a token fromclient application 152 that follows a request to access a namespace andcan return the capabilities permitted to the user account. For useraccounts with multiple levels of access (e.g. a user account with userrights and administrator rights) authorization service 132 can alsorequire explicit privilege escalation to avoid unintentional actions byadministrators.

Presence and Seen State

In some embodiments, content management system can provide informationabout how users with which a content item is shared are interacting orhave interacted with the content item. In some embodiments, contentmanagement system 110 can report that a user with which a content itemis shared is currently viewing the content item. For example, clientcollaboration service 160 can notify notifications service 117 whenclient device 150 is accessing the content item. Notifications service117 can then notify all client devices of other users having access tothe same content item of the presence of the user of client device 150with respect to the content item.

In some embodiments, content management system 110 can report a historyof user interaction with a shared content item. Collaboration service126 can query data sources such as metadata database 146 and server filejournal 148 to determine that a user has saved the content item, that auser has yet to view the content item, etc., and disseminate this statusinformation using notification service 117 to other users so that theycan know who currently is or has viewed or modified the content item.

Collaboration service 126 can facilitate comments associated withcontent, even if a content item does not natively support commentingfunctionality. Such comments can be stored in metadata database 146.

Collaboration service 126 can originate and transmit notifications forusers. For example, a user can mention another user in a comment andcollaboration service 126 can send a notification to that user that hehas been mentioned in the comment. Various other content item events cantrigger notifications, including deleting a content item, sharing acontent item, etc.

Collaboration service 126 can provide a messaging platform whereby userscan send and receive instant messages, voice calls, emails, etc.

Collaboration Content Items

In some embodiments content management service can also includeCollaborative document service 134 which can provide an interactivecontent item collaboration platform whereby users can simultaneouslycreate collaboration content items, comment in the collaboration contentitems, and manage tasks within the collaboration content items.Collaboration content items can be files that users can create and editusing a collaboration content item editor, and can contain collaborationcontent item elements. Collaboration content item elements may include acollaboration content item identifier, one or more author identifiers,collaboration content item text, collaboration content item attributes,interaction information, comments, sharing users, etc. Collaborationcontent item elements can be stored as database entities, which allowsfor searching and retrieving the collaboration content items. Multipleusers may access, view, edit, and collaborate on collaboration contentitems at the same time or at different times. In some embodiments thiscan be managed by requiring two users access a content item through aweb interface and there they can work on the same copy of the contentitem at the same time.

Collaboration Companion Interface

In some embodiments client collaboration service 160 can provide anative application companion interface for the purpose of displayinginformation relevant to a content item being presented on client device150. In embodiments wherein a content item is accessed by a nativeapplication stored and executed on client device 150, where the contentitem is in a designated location of the file system of client device 150such that the content item is managed by content application 152, thenative application may not provide any native way to display the aboveaddressed collaboration data. In such embodiments, client collaborationservice 160 can detect that a user has opened a content item, and canprovide an overlay with additional information for the content item,such as collaboration data. For example, the additional information caninclude comments for the content item, status of the content item,activity of other users previously or currently viewing the contentitem. Such an overlay can warn a user that changes might be lost becauseanother user is currently editing the content item.

In some embodiments, one or more of the services or storages/databasesdiscussed above can be accessed using public or private applicationprogramming interfaces.

Certain software applications can access content storage 142 via an APIon behalf of a user. For example, a software package such as anapplication running on client device 150, can programmatically make APIcalls directly to content management system 110 when a user providesauthentication credentials, to read, write, create, delete, share, orotherwise manipulate content.

A user can view or manipulate content stored in a user account via a webinterface generated and served by web interface service 124. Forexample, the user can navigate in a web browser to a web addressprovided by content management system 110. Changes or updates to contentin the content storage 142 made through the web interface, such asuploading a new version of a content item, can be propagated back toother client devices associated with the user's account. For example,multiple client devices, each with their own client software, can beassociated with a single account and content items in the account can besynchronized between each of the multiple client devices.

Client device 150 can connect to content management system 110 on behalfof a user. A user can directly interact with client device 150, forexample when client device 150 is a desktop or laptop computer, phone,television, internet-of-things device, etc. Alternatively oradditionally, client device 150 can act on behalf of the user withoutthe user having physical access to client device 150, for example whenclient device 150 is a server.

Some features of client device 150 are enabled by an applicationinstalled on client device 150. In some embodiments, the application caninclude a content management system specific component. For example, thecontent management system specific component can be a stand-aloneapplication 152, one or more application plug-ins, and/or a browserextension. However, the user can also interact with content managementsystem 110 via a third-party application, such as a web browser, thatresides on client device 150 and is configured to communicate withcontent management system 110. In various implementations, theclient-side application 152 can present a user interface (UI) for a userto interact with content management system 110. For example, the usercan interact with the content management system 110 via a file systemexplorer integrated with the file system or via a webpage displayedusing a web browser application.

In some embodiments, client application 152 can be configured to manageand synchronize content for more than one account of content managementsystem 110. In such embodiments client application 152 can remain loggedinto multiple accounts and provide normal services for the multipleaccounts. In some embodiments, each account can appear as folder in afile system, and all content items within that folder can besynchronized with content management system 110. In some embodiments,client application 152 can include a selector to choose one of themultiple accounts to be the primary account or default account.

While content management system 110 is presented with specificcomponents, it should be understood by one skilled in the art, that thearchitectural configuration of system 100 is simply one possibleconfiguration and that other configurations with more or fewercomponents are possible. Further, a service can have more or lessfunctionality, even including functionality described as being withanother service. Moreover, features described herein with respect to anembodiment can be combined with features described with respect toanother embodiment.

While system 100 is presented with specific components, it should beunderstood by one skilled in the art, that the architecturalconfiguration of system 100 is simply one possible configuration andthat other configurations with more or fewer components are possible.

Client Synchronization Service

FIG. 2 shows an example of a client synchronization service 156, inaccordance with some embodiments. According to some embodiments, clientsynchronization service 156 may be implemented in the client device ofFIG. 1. However, in other embodiments, client synchronization service156 may be implemented on another computing device. Clientsynchronization service 156 is configured to synchronize changes tocontent items between a content management system and the client deviceon which client synchronization service 156 runs.

Client synchronization service 156 may include file system interface205, server interface 210, tree storage 220, planner 225, and scheduler230. Additional or alternative components may also be included. Highlevel descriptions of client synchronization service 156 and itscomponents are discussed below with respect to FIG. 2. However, furtherdetails and embodiments of client synchronization service 156 and itscomponents are discussed throughout.

File system interface 205 is configured to process changes to contentitems on the local filesystem of the client device and update the localtree. For example, file system interface 205 can be in communicationwith client synchronization service 156 of FIG. 1 detect changes tocontent items on the local filesystem of the client device. Changes mayalso be made and detected via client application 152 of FIG. 1. Filesystem interface 205 may make updates to the local tree may be madebased on the changes (new, deleted, modified, copied, renamed, or movedcontent items) to content items on the client device.

Server interface 210 is configured to aid in the processing of remotechanges to content items at a remote storage of the content managementsystem and updating of the remote tree. For example, server interface210 can be in communication with server synchronization service 112 ofFIG. 1 to synchronize changes to content items between client device 150and content management system 110. Changes (new, deleted, modified,copied, renamed, or moved content items) to content items at contentmanagement system 110 may be detected and updates may be made to theremote tree to reflect the changes at content management system 110.

Tree storage 220 is configured to store and maintain the tree datastructures used by client synchronization service 156. For example, treestorage 220 may store the local tree, the sync tree, and the remotetree. According to some embodiments, tree storage 200 may store the treedata structures in persistent memory (e.g., a hard disk or othersecondary storage device) as well as in main memory (e.g., RAM or otherprimary storage device) in order to reduce latency and response time.For example, on start-up of the client device or client synchronizationservice 156, the tree data structures may be retrieved from persistentmemory and loaded into main memory. Tree storage 220 may access andupdate the tree data structures on main memory and, before the clientdevice or client synchronization service 156 is shut down, tree storage220 may store the updated tree data structures on persistent memory.Because main memory is expensive in cost and often limited in size onmost client devices, additional technological improvements areimplemented to decrease the footprint of the tree data structures onmain memory. These technological solutions are described further below.

Planner 225 is configured to detect differences between the server stateassociated with the content management system and the file system stateassociated with the client device based on the state of the tree datastructures. For example, planner 225 may determine if there is adifference between the remote tree and the sync tree. A differencebetween the remote tree and the sync tree indicates that an actionperformed remotely on one or more content items stored at the contentmanagement system has caused the server state and the file system stateto become out of sync. Similarly, planner 225 may also determine ifthere is a difference between the local tree and the sync tree. Adifference between the local tree and the sync tree indicates that anaction performed locally on one or more content items stored on theclient device has caused the server state and the file system state tobecome out of sync. If a difference is detected, planner 225 generates aset of operations that synchronize the tree data structures.

In some scenarios, a set of operations generated based on a differencebetween the remote tree and the sync tree and a set of operationsgenerated based on a difference between the local tree and the sync treemay conflict. Planner 225 is may also be configured to merge the twosets of operations into a single merged plan of operations.

Scheduler 230 is configured to take the generated plan of operations andmanage the execution of those operations. According to some embodiments,scheduler 230 converts each operation in the plan of operations into aseries of one or more tasks that need to be executed in order to performthe operation. In some scenarios, some tasks may become out dated or nolonger relevant. Scheduler 230 is configured to identify those tasks andcancel them.

Tree Data Structures

FIG. 3 shows an example of tree data structures, in accordance withvarious embodiments. The tree data structures may be stored at theclient device and managed by a client synchronization service such asclient synchronization service 156 in FIG. 2. In FIG. 3, the tree datastructures are shown including remote tree 310, sync tree 330, and localtree 350.

Remote tree 310 represents a server state or the state of content itemsstored remotely from the client device (e.g., on a server of the contentmanagement system). Local tree 350 represents a file system state or thestate of the corresponding content items stored locally on the clientdevice. Sync tree 330 represents a merge base for the local tree and theremote tree. The merge base may be thought of as a common ancestor ofthe local tree and the remote tree or a last known synced state betweenthe local tree and the remote tree.

Each tree data structure (e.g., remote tree 310, sync tree 330, or localtree 350) may include one or more nodes. Each node may have one or morechild nodes and the parent-child relationship is represented by an edge.For example, remote tree 310 includes nodes 312 and 314. Node 312 is aparent of node 314 and node 314 is a child of node 312. Thisparent-child relationship is represented by edge 316. A root node, suchas root node 312, does not have a parent node. A leaf node, such as node314, does not have a child node.

Each node in a tree data structure may represent a content item (e.g., afile, document, folder, etc.). For example, root node 312 may representthe root folder associated with the content management system and node314 may represent a file (e.g., a text file named “Foo.txt”) located inthat root folder. Each node in a tree data structure may contain datasuch as, for example, a directory file identifier (“DirFileID”)specifying the file identifier of a parent node of the content item, afile name for the content item, a file identifier for the content item,and metadata for the content item. In some embodiments each node in atree data structure may be keyed or referenced by its file identifierand have a unique path from the root to the node.

As described above, a client synchronization service may determine thatthe server state and the file system state of the client device aresynchronized when all 3 trees (e.g., remote tree 310, sync tree 330, andlocal tree 350) are identical. In other words, the trees are in syncwhen their tree structures and the relationships that they express areidentical and the data contained in their nodes are identical as well.Conversely, the trees are not in sync if the 3 trees are not identical.In the example scenario illustrated in FIG. 3, remote tree 310, synctree 330, and local tree 350 are shown as being identical and in syncand, as a result, the server state and the file system state aresynchronized.

Tracking Changes Using Tree Data Structures

FIG. 4 shows an example of tree data structures, in accordance withvarious embodiments. As with the tree data structures shown in FIG. 3,the tree data structures shown in FIG. 4 (including remote tree 410,sync tree 430, and local tree 450) may be stored at the client deviceand managed by a client synchronization service such as clientsynchronization service 156 in FIG. 2. In FIG. 3, the tree datastructures are shown.

FIG. 4 shows a scenario after a previously synchronized state, such asthe scenario illustrated in FIG. 3, additional actions are performed onthe content items represented in the trees to modify the content itemssuch that the trees are no longer in sync. Sync tree 430 maintains arepresentation of the previously known synchronized state and may beused by the client synchronization service to identify the differencesbetween the server state and the file system state as well as generateoperations for the content management system and/or the client device toperform to converge so that the server state and the file system stateare synchronized.

For example, a user (the same user as the user associated with theclient device or a different user with access to the content item) maymake modifications to the “foo.txt” content item stored by the contentmanagement system. This content item is represented by node 414 inremote tree 410. The modification shown in the remote tree 410 is aremoval (e.g., a removal of the content item from a space managed by thecontent management system) or delete of the foo.txt content item. Thesemodifications may be performed, for example, on another client deviceand the modifications were synced to the content item stored by thecontent management system or content item stored by the contentmanagement system via a web browser.

When the change is made on the content management system, the contentmanagement system generates modification data specifying the change madeand transmits the modification data to the client synchronizationservice on the client device. The client synchronization service updatesthe remote tree representing the server state for the content itemsstored by the content management system based on the modification data.For example, in remote tree 410, node 414 representing the foo.txtcontent item is shown as deleted.

The client synchronization service may identify a difference betweenremote tree 410 and sync tree 430 and, as a result, determine that amodification of the content items at the content management system hascaused the server state and the file system state to no longer be insync. The client synchronization service may further generate andexecute a set or sequence of operations for the content items stored onthe client device that are configured to converge the server state andthe file system state so that they will be in sync.

Additionally or alternatively, a user (the same user as the userassociated with modifications at the content management system or adifferent user with access to the content item) may make modificationsto the content items stored locally on the client device that areassociated with the content management system. For example, the user mayadd a folder “/bar” to the “/root” folder and add a “Hi.doc” document tothe “/bar” folder.

When the change is made on the client device, the client device (e.g.,client synchronization service 156 or client application 152 of FIG. 1)generates modification data specifying the change made and passes themodification data to the client synchronization service on the clientdevice. The client synchronization service updates the local treerepresenting the file system state for the content items stored on theclient device based on the modification data. For example, in local tree450, node 452 and node 454 are shown as added. Node 452 and node 454represent the “/bar” folder and the “Hi.doc” document respectively.

The client synchronization service may identify a difference betweenlocal tree 450 and sync tree 430 and, as a result, determine that amodification of the content items at the client device has caused theserver state and the file system state to no longer be in sync. Theclient synchronization service may further generate a set or sequence ofoperations for the content items stored by the content management systemthat are configured to converge the server state and the file systemstate so that they will be in sync. These operations may be transmittedto the content management system for execution.

As seen in FIG. 4, modifications to content items stored on the clientdevice and content items stored by the content management system mayoccur at substantially the same time or within a particular time period.These modifications can be reflected in the tree data structures andused by the client synchronization service to generate operations forthe client device and for the content management system in parallel. Inother scenarios, however, modifications may not necessarily occur withinthe same time period and operations may be generated in an as-neededmanner. Furthermore, although FIG. 4 illustrates scenarios for addingcontent items and deleting content items, other types of modificationssuch as, editing, renaming, copying, or moving content items are alsosupported.

According to various embodiments, identifying a difference between twotree data structures and generating operations may involve checking eachnode in both tree data structures and determining whether an action hasbeen performed on the node. The actions may include, for example, theaddition of the node, the deletion of the node, the editing of the node,or the moving of the node. These actions may then be used to generatethe operations configured to converge the server state and the filesystem state.

For example, if the two tree data structures are a sync tree and aremote tree, the client synchronization service may identify each nodein the sync tree by, for example, requesting the file identifiers of allnodes in the sync tree. For each node or file identifier for the node inthe sync tree, the client synchronization service may determine if thenode or file identifier is also in the remote tree. A node or fileidentifier in the sync tree that is not found in the remote tree mayindicate that the node has been deleted from the server state that isrepresented by the remote tree. Accordingly, the client synchronizationservice may determine that a delete action has occurred on the remotetree. If the node or file identifier for the node is found in the remotetree, the client synchronization service may check whether the node inthe remote tree has been edited or moved.

To determine whether the node in the remote tree has been edited withrespect to the node in the sync tree, the client synchronization servicemay compare the metadata for the node in the sync tree with the metadatafor the corresponding node (e.g., the node with the same fileidentifier) in the remote tree. The metadata may include informationthat may be used to determine whether the content item represented bythe node has been edited. For example, the metadata may include one ormore hash values that are generated based on the data in the contentitem or a portion thereof. The metadata may additionally oralternatively include a size value, a last modified value, or othervalue for the content item. The metadata for the node in the sync treemay be compared with the metadata for the node in the remote tree. Ifthe metadata do not match, an edit of the content item may have beenedited in the server state represented by the remote tree. Accordingly,the client synchronization service may determine that an edit action hasoccurred for the node on the remote tree. If the metadata matches, noedit may have occurred.

To determine whether the node in the remote tree has been moved, theclient synchronization service may compare the location for the node inthe sync tree with the location for the corresponding node (e.g., thenode with the same file identifier) in the remote tree. The location mayinclude, for example, a path where the node is located, a file name,and/or a directory file identifier (“DirFileID”) specifying the fileidentifier of the node's parent. If the locations match, no move mayhave occurred. On the other hand, if the locations do not match, a moveof the content item may have occurred in the server state represented bythe remote tree. Accordingly, the client synchronization service maydetermine that a move action has occurred for the node on the remotetree.

To determine whether a node has been added to the remote tree, theclient synchronization service may identify any nodes or fileidentifiers in the remote tree that are not found in the sync tree. If anode or file identifier is found in the remote tree and not found in thesync tree, the client synchronization service may determine that an addaction of this node has occurred on the remote tree representing theserver state.

Although the example above is described with respect to the sync treeand the remote tree, in other embodiments, a similar process may occurwith the sync tree and a local tree in order to identify a differencebetween the sync tree and the local tree and determine which actionshave occurred on the local tree representing the file system state.

Synchronization Using Tree Data Structures

FIG. 5 shows an example method for synchronizing a server state and afile system state using tree data structures, in accordance with variousembodiments of the subject technology. Although the methods andprocesses described herein may be shown with certain steps andoperations in a particular order, additional, fewer, or alternativesteps and operations performed in similar or alternative orders, or inparallel, are within the scope of various embodiments unless otherwisestated. The method 500 may be implemented by a system such as, forexample, client synchronization service 156 of FIG. 2, running on aclient device.

The system is configured to identify a difference between a remote treerepresenting a server state for content items stored by the contentmanagement system, a local tree representing the file system state forthe corresponding content items stored on the client device, and a synctree representing a known synced state between the server state and thefile system state. Based on these differences, a set of operations maybe generated that, if executed, are configured to converge the serverstate and the file system state towards a synchronized state where thethree tree data structures would be identical.

For example, at operation 505, the system may receive modification datafor content items stored by a content management system or on a clientdevice. The modification data may be used to update a remote tree or alocal tree at operation 510.

The modification data is specifies what changes are done to one or morecontent items associated with a content management service. Accordingly,the modification data may be received from the content management systemor from the client device (e.g., from client application 152 running onclient device 150 in FIG. 1). Modification data received from thecontent management system may be referred to as server modificationdata. Server modification data specifies what changes are done to one ormore content items by the content management system and may be used toupdate the remote tree at operation 510. Modification data received fromthe client device may be referred to as client modification data. Clientmodification data specifies what changes are done to one or more contentitems on the client device and may be used to update the local tree atoperation 510.

At operation 515, the system may determine whether a server state forcontent items stored by the content management system and a file systemstate for the content items stored on the client device are in sync.Because the local tree and the remote tree are representative of thefile system state and the server state and are continually being updatedto track changes that occur at the content management system and theclient device, determining whether the server state and the file systemstate are in sync may be done by comparing the local tree and/or theremote tree to the sync tree to find differences between the trees. Thisprocess of finding differences between the trees is sometimes referredto as “diffing” the trees.

According to some embodiments and scenarios, determining whether theserver state and the file system state are in sync may include one ormore of identifying differences between the remote tree and the synctree and/or identifying differences between the local tree and the synctree. Differences between the remote tree and sync tree may indicate theoccurrence of changes to content items stored by the content managementsystem that may not be reflected at the client device. Similarly,differences between the local tree and sync tree may indicate theoccurrence of changes to content items stored at the client device thatmay not be reflected at the content management system.

If there are no differences between the trees, the server state and thefile system state are in sync and no synchronization actions are needed.Accordingly, the method may return to operation 505 and await newmodification data. On the other hand, if differences are detected, thesystem may generate a set of operations configured to converge theserver state and the file system state at operation 520.

The set of operations generated depends on the one or more differencesthat are detected. For example, if the difference between two trees isan added content item, the generated set of operations may includeretrieving the added content item and adding it. If the differencebetween two trees is a deletion of a content item, the generated set ofoperations may include deleting the content item. According to someembodiments, the set of operations may also include a number of checksto ensure tree constraints are maintained. As will be described furtherbelow, the set of operations may conflict with the current state of theserver state, the file system state, or other operations that arepending execution. Accordingly, the system may also resolve theseconflicts before proceeding.

As noted above, if there are differences between the remote tree andsync tree, changes to content items stored by the content managementsystem may have occurred that may not be reflected at the client device.Accordingly, in this scenario, the system may generate a client set ofoperations configured to operate on the content items stored on theclient device to converge the server state and the file system state andthis client set of operations may be provided to the client device forexecution at operation 525.

On the other hand, if there are differences between the local tree andsync tree, changes to content items stored at the client device may haveoccurred that may not be reflected at the content management system.Accordingly, in this scenario, the system may generate a server set ofoperations configured to operate on the content items stored by thecontent management system to converge the server state and the filesystem state and this server set of operations may be provided to thecontent management system for execution at operation 525. In some cases,both cases may be true and a client set of operations and a server setof operations may be generated and provided to their intended recipientsat operation 525.

Once the set(s) of operations are provided to the intended recipient(s),the method may return to operation 505 and await new modification data.The set(s) of operations may provide one or more steps towards theconvergence of the server state and the file system state or provide allsteps needed to sync the server state and the file system state. Forexample, the content management system may receive the server set ofoperations and execute the server set of operations on content itemsstored by the content management system. This execution of the serverset of operations causes changes to the content items stored by thecontent management system, which are detected and specified in servermodification data, which is transmitted back to the system. The systemmay then update the remote tree and determine whether the server stateand the file system state are in sync.

The client device may receive the client set of operations and executethe client set of operations on content items stored on the clientdevice. This execution of the client set of operations causes changes tothe content items stored on the client device, which are detected andspecified in client modification data, which is passed to the system.The system may then update the local tree and determine whether theserver state and the file system state are in sync. These operations ofmethod 500 may continue until the server state and the file system stateare in sync.

The operations of method 500 are described with respect to a client sideand a server side (e.g., a local tree and a remote tree, a file systemstate and a server state, a client set of operations and a server set ofoperations, client modification data and server modification data). Invarious embodiments the operations associated with the two sides mayoccur in parallel, in sequence, in isolation of the other side, or acombination.

As will be discussed in further detail, in accordance with someembodiments, before the operations are provided for execution, thesystem may check the operations to determine whether they comply with aset of rules or invariants. If an operation violates a rule, the systemexecutes a resolution process associated with the violation of the rule.

Additionally, in accordance with some embodiments, the system (e.g.,scheduler 230 of client synchronization service 156 in FIG. 2) maymanage the execution of the set of operations. For example, eachoperation in the set of operations may be associated with a task, anexecution thread, series of steps, or instructions. The system may beconfigured to execute the task, thread, step, or instructions andinterface with the client device and/or the content management system toexecute the set of operations and converge the server state and the filesystem state.

Conflict Handling

As described above with respect to FIG. 5, differences between a synctree and a remote tree are identified and used to generate a client setof operations configured to converge the server state and the filesystem state. However, in some cases, the client set of operations mayconflict with the current state of a local tree. Similarly, differencesbetween the sync tree and the local tree are identified and used togenerate a server set of operations configured to converge the serverstate and the file system state. However, the server set of operationsmay conflict with the current state of the remote tree. Additionally oralternatively, the client set of operations and the server set ofoperations may conflict with one another or violate another rule orinvariant maintained by the system. Accordingly, various embodiments ofthe subject technology provide additional technical improvements byresolving these conflicts.

For example, planner 225 in client synchronization service 156 of FIG. 2may identify an operation in a set of operations (e.g., the client setof operations or the server set of operations) that conflicts with arule. Each rule used to identify a conflict may also be associated witha resolution for the conflict. The client synchronization service mayupdate the set of operations based on the resolution for the conflict orperform resolve the conflict by performing operations associated withthe resolutions for the conflict before providing the set of operationsfor execution.

FIG. 6 shows an example method 600 for resolving conflicts whensynchronizing a server state and a file system state using tree datastructures, in accordance with various embodiments of the subjecttechnology. Although the methods and processes described herein may beshown with certain steps and operations in a particular order,additional, fewer, or alternative steps and operations performed insimilar or alternative orders, or in parallel, are within the scope ofvarious embodiments unless otherwise stated. The method 600 may beimplemented by a system such as, for example, client synchronizationservice 156 of FIG. 2, running on a client device.

The system may receive a set of operations configured to converge aserver state and a file system state at operation 620. The set ofoperations may be, for example, the client set of operations, the serverset of operations, or a combined set of operations generated anddescribed with respect to the method 500 of FIG. 5.

At operation 650, the system identifies one or more violations in theset of operations based on a set of rules. The set of rules may bestored by client synchronization service 156 in FIG. 2 and specify anumber of constraints, invariants, or conflicts for operations that areto be resolved. The set of rules may be applied to the tree datastructures and help control sync behavior. Each rule in the set of rulesmay also be associated or otherwise linked to a resolution to aviolation of that rule. For example, the resolution may include analteration of one or more operations in the set of operations, a removaloff one or more operations, an addition of one or more operations, oneor more additional actions to the server state or the file state, or acombination of actions.

For each operation in a set of operations, the system may determinewhether any rule in the set of rules is violated. If a rule is violated,the system identifies a resolution of the violation and, at operation655, performs the resolution. The resolution may include actions such asmodifying one or more operations in the set of operations, a removing oradding one or more operations, or additional actions on the server stateor the file state.

Once the resolution actions are performed, the system may generate aresolved or rebased set of operation based on the resolution and the setof operations at operation 660 and, at operation 665, provide theresolved set of operations to the appropriate entity for execution. Forexample, the resolved set of operations may be provided to scheduler 230of client synchronization service 146 in FIG. 2 for managed execution.Alternatively, if the set of operations is a client set of operations,the resolved set of operations may be provided to the client device. Ifthe set of operations is a server set of operations, the resolved set ofoperations may be provided to the content management service.Additionally, the method 600 of FIG. 6 may be performed on client set ofoperations and server set of operations in sequence, in parallel, or invarious different orders.

According to some embodiments, each type of operation may be associatedwith the same or a different set of rules. For example, operation typesmay include, for example, adding a content item, deleting a contentitem, editing a content item, moving a content item, renaming a contentitem, etc. The set of operations may consist of operations eachbelonging to one of the operation types above. Each operation type maybe associated with a specific set of rules.

For illustrative purposes, a set of rules for an “Add” operation typemay include rules such as file identifiers for content items must beunique in a tree (e.g., no two nodes in a tree may have the same fileidentifier), a directory file identifier (“DirFileID”) specifying thefile identifier of a parent node of the content item must exist in theopposite tree data structure, and a DirFileID and file name combinationfor a content item are not used in the opposite tree.

Opposite tree, as used here, refers to the tree data structure thatrepresents the state of the opposing entity. For example, a client setof operations configured to operate on the client device and theresulting changes to the file system on the client device will bereflected in the local tree. Accordingly, the opposite tree for theclient set of operations is the remote tree. Similarly, a server set ofoperations is configured to be transmitted to the content managementsystem to be executed and the resulting changes to the server state willbe reflected in the remote tree. Accordingly, the opposite tree for theserver set of operations is the local tree.

FIG. 7 shows an example of tree data structures illustrating a violationof a rule for an add operation, in accordance with various embodiments.The tree data structures include remote tree 710, sync tree 750, andlocal tree 770. When referencing the local tree 770, the remote tree 710may be considered the opposite tree. On the other hand, when referencingthe remote tree 710, the local tree 770 may be considered the oppositetree. FIG. 7 illustrates a set of operations adding the content itemrepresented by node 712 in remote tree 710. For example, a clientsynchronization service may compare remote tree 710 with sync tree 750,identify the differences, and generate a set of operations that includesthe addition of node 712. Node 712 is associated with a FileID of 4, aDirFileID of 3 (which references parent node 714, which is node 712'sparent), and a file name of “Hi.” Parent node 714 is associated with aFileID of 3, a DirFileID of 1 (which references root node 716, which isnode 714's parent), and a file name of “Foo.”

The client synchronization service may perform the method 600 of FIG. 6and determine that the add operation for node 712 violates the “adirectory file identifier (“DirFileID”) of the content item must existin the opposite tree data structure” rule for “add” operation types.This is illustrated in FIG. 7 by the local tree 770 not having a nodewith a file ID of 3, which references parent node 714 of node 712. Thismay occur when, for example, after differences between remote tree 710and sync tree 750 are determined and a set of operations is generated,the “Foo” node corresponding to node 714 is removed from the oppositetree.

The resolution associated for this rule may include deleting the nodemissing from local tree 770 from sync tree 750 to synchronize sync tree750 and local tree 770 and rediffing (e.g., finding the differencebetween) remote tree 710 and sync tree 750. In the scenario illustratedin FIG. 7, node 754 in sync tree 750 would be removed 758 and diffingoperations would commence to identify differences between remote tree710 and sync tree 750. This would result in the inclusion of an addoperation of node 714 as well as an add operation for node 712 in theset of operations.

Similarly, a violation of the “file identifiers for content items mustbe unique in a tree” rule for “add” operation types may be resolved byoperations including requesting, from the content management system, anew file ID for the node being added and using the new file ID whenadding the node. A violation of the “DirFileID and file name combinationfor a content item are not used in the opposite tree” rule for “add”operation types may be resolved by operations including checking via themetadata associated with the two nodes whether the content items are thesame. If the content items are the same, it is likely that the contentitem being added has already been added in other actions. If the contentitems are not the same, the file name for the content item being addedcan be renamed. For example, the file name for the content item beingadded can be appended with the text “(conflicted version).”

Incremental Planner

Although the various tree data structures shown in FIGS. 3, 4, and 7contain a relatively small number of nodes and are relatively simple instructure, the tree data structures supported by the system may be muchlarger and complex with multiple levels and potentially large number ofnodes at each level. Accordingly the memory usage required to store thetree data structures during operation may be quite large and thecomputing time and resources required to operate on the tree datastructures may be quite large. For example, finding differences betweena remote tree and a sync tree and/or a local tree and the sync tree andgenerating operations needed to converge the remote tree and the synctree and/or the local tree and the sync tree may require a large amountof memory, time, and other computing resources.

Unfortunately, these computing resources are limited. For example, aclient device may have a limited amount of available memory and thelength of time needed to diff trees and generate operations may hinderthe usability of the client device, the client application, or thecontent management service provided by the content management system.Furthermore, the more time needed to converge the server state and thefile system state, the more likely that intervening changes to eitherstate may render the set of operations being computed or executed and/orthe target sync state out of date. Accordingly, various embodiments ofthe subject technology provide additional technical improvements byincrementally converging the server state and the file system statealong with the tree data structures that represent them.

FIG. 8 shows an example method 800 for incrementally converging a serverstate and a file system state, in accordance with various embodiments ofthe subject technology. Although the methods and processes describedherein may be shown with certain steps and operations in a particularorder, additional, fewer, or alternative steps and operations performedin similar or alternative orders, or in parallel, are within the scopeof various embodiments unless otherwise stated. The method 800 may beimplemented by a system such as, for example, client synchronizationservice 156 of FIG. 2, running on a client device.

At operation 805, the system may receive modification data that may beused to update either a remote tree or a local tree. For example, servermodification data may be received from a content management service andspecify modifications or other actions (e.g., an edit, add, delete,move, or rename) associated with one or more content items stored by thecontent management system. The server modification data may be used toupdate the remote tree, which represents the server state of contentitems stored by the content management system. Similarly, clientmodification data may be received from the client device (e.g., a clientapplication) and specify modifications or other actions associated withone or more content items stored on the client device. The clientmodification data may be used to update the local tree, which representsthe file system state of content items stored on the client device.

Based on the received modification data specifying modificationsassociated with content items, the system may identify nodes thatcorrespond to the modified content items and add the nodes to a list ofmodified content items (e.g., add the file identifier associated withthe nodes to the list of modified content items) at operation 810.Operations 805 and 810 may continuously occur for some time before thesystem proceeds to the next stage of the method 800. For exampleadditional modification data may be received and used to update thetrees managed by the system and add nodes to the list of modifiedcontent items.

In order to incrementally converge the server state and the file systemstate, the system takes each node in the list of modified content itemsand determines how the node was modified (e.g., which actions areassociated with the node) at operation 815. In some embodiments, themodification data may specify the modification to the node. However, inother embodiments, the system may determine the modifications to thenode based on a comparison of the remote tree with the sync tree and/ora comparison of the local tree with the sync tree. For example, themodifications may include the addition of the node, the deletion of thenode, the editing of the node, or the moving of the node.

For each node or file identifier for the node in the list of modifiedcontent items, the system may perform a series of checks to determinewhat, if any, modifications were performed on the node. For example, thesystem may determine whether the file identifier is in the sync tree butnot in the remote tree. A file identifier in the sync tree that is notfound in the remote tree may indicate that the node has been deletedfrom the server state that is represented by the remote tree.Accordingly, the client synchronization service may determine that adelete modification on the node has occurred on the remote tree.Similarly, the system may also determine whether the file identifier isin the sync tree but not in the local tree. A file identifier in thesync tree that is not found in the local tree may indicate that the nodehas been deleted from the file system state that is represented by thelocal tree. Accordingly, the client synchronization service maydetermine that a delete modification on the node has occurred on thelocal tree.

To determine whether an edit modification has been performed on the nodethe system may compare the metadata for the node in the sync tree withthe metadata for the corresponding node (e.g., the node with the samefile identifier) in the remote tree and/or the local tree. The metadatamay include information that may be used to determine whether thecontent item represented by the node has been edited. For example, themetadata may include one or more hash values that are generated based onthe data in the content item or a portion thereof. The metadata mayadditionally or alternatively include a size value, a last modifiedvalue, or other value for the content item. If the metadata do notmatch, an edit of the content item may have been edited in the serverstate represented by the remote tree and/or the file system staterepresented by the local tree. Accordingly, the system may determinethat an edit action has occurred for the node on the remote tree and/orthe local tree.

To determine whether the node in the remote tree has been moved, thesystem may compare the location for the node in the sync tree with thelocation for the corresponding node (e.g., the node with the same fileidentifier) in the remote tree and/or the local tree. The location mayinclude, for example, a path where the node is located, a file name,and/or a directory file identifier (“DirFileID”) specifying the fileidentifier of the node's parent. If the locations match, no move mayhave occurred. On the other hand, if the locations do not match, a moveof the content item may have occurred in the remote tree or the localtree. Accordingly, the client synchronization service may determine thata move action has occurred for the node on the remote tree and/or thelocal tree.

To determine whether a node has been added to the remote tree, thesystem may determine if the file identifier in the list of modifiedcontent items is in the remote tree or in the local tree, but not in thesync tree. If the file identifier is found in the remote tree or thelocal tree and not found in the sync tree, the system may determine thatan add modification for this node has occurred.

Once the one or more modifications to the nodes in the list of modifiedcontent items are determined, the system may determine whether any ofthose modifications have dependencies at operation 820. As will beillustrated further with respect to FIG. 9, a modification on a node hasa dependency when, for example, the modification cannot execute withoutanother modification occurring first.

If the modification does not have a dependency, the system adds themodification to an unblocked list of actions at operation 825. If themodification has a dependency, the modification is blocked for the timebeing at operation 830 and cannot be executed without anothermodification being processed first. After each of the modifications areprocessed, the system may clear the file identifiers associated with themodifications from the list of modified content items.

FIG. 9 shows an example of tree data structures, in accordance withvarious embodiments. The tree data structures shown in FIG. 9 may bestored at the client device and managed by a system such as clientsynchronization service 156 in FIG. 2. For the purpose of illustration,only remote tree 910 and sync tree 950 are shown in FIG. 9 anddescribed. Similar operations and description may also be applied to alocal tree as well.

Remote tree 910 includes root node 912 with a file identifier of 1, node914 with a file identifier of 5 and file name of “Foo,” node 916 with afile identifier of 6 and file name of “Bar,” and node 918 with a fileidentifier of 7 and file name of “Bye.” Sync tree includes root node 952with a file identifier of 1.

Based on the tree data structures shown in FIG. 9, the system may haveidentified that nodes with file identifiers of 5, 6, and 7 have beenmodified at operation 810 and added the nodes to the list of modifiedcontent items, as illustrated by reference 980 in FIG. 9. At operation815, the system determines the list of modifications to nodes in thelist of modified content items. As is seen by the comparison of remotetree 910 and sync tree 950, nodes 914, 916, and 918 have been added toremote tree 910. More specifically, as illustrated by reference 982 inFIG. 9, node 916 with file identifier 6 and name “Bar” has been added asa child to node 914 with file identifier 5. This is represented by the“Add(6, 5, Bar)” entry in reference 982. Node 918 with file identifier 7and name “Bye” has been added as a child to node 914 with fileidentifier 5. This is represented by the “Add(7, 5, Bye)” entry inreference 982. Node 914 with file identifier 5 and name “Foo” has beenadded as a child to root node 912 with file identifier 1. This isrepresented by the “Add(5, /root, Foo)” entry in reference 982.

At operation 820, the system determines that the add modification ofnode 914 does not have a dependency and, as a result, is unblocked.Accordingly, the system adds the modification associated with node 914(e.g., the modification represented by the “Add(5, /root, Foo)”) entryin reference 982) to an unblocked list of actions at operation 825. Thisis seen in references 984 in FIG. 9. On the other hand, themodifications for nodes 916 and 918 represented by the “Add(6, 5, Bar)”and the “Add(7, 5, Bye)” entries in reference 982 are dependent on themodification represented by the “Add(5, /root, Foo)” occurring first. Inother words, node 916 and/or node 918 cannot be added until node 914 isadded. Accordingly, these modifications are included in a blocked listof actions illustrated by reference 986 in FIG. 9.

Returning to the method 800 of FIG. 8, at operation 835, the system mayselect a set of modifications from the unblocked list of actions andgenerate a set of operations based on the selected set of modifications.The set of operations is configured to converge the server state and thefile system state. The set of operations generated depends on theselected set of modifications from the unblocked list. For example, ifthe selected set of modifications includes the add modificationassociated with node 914 (e.g., the modification represented by the“Add(5, /root, Foo)”) entry in reference 984) in FIG. 9, the generatedset of operations may include retrieving the added content item from thecontent management system and adding it to the local file system of theclient device.

According to some embodiments, the system may select all modificationsfrom the unblocked list of actions to generate one or more sets ofoperations. However, in some scenarios, the number of modifications inthe unblocked list may be quite high and the computing resources (e.g.,memory and processing time) needed to process all of the modificationsis substantial. In order to reduce these technological burdens, thesystem may select a smaller set of the modifications in the unblockedlist of actions in order to process incrementally. For example, thesystem may select the first or top X number or percent of modificationsto generate operations. In further iterations of the process, theremaining modifications in the unblocked lists may be processed.

In some embodiments, the modifications in the unblocked list may beranked for processing. The modifications may be ranked based on, forexample, a modification type (e.g., delete modifications are prioritizedover add modifications), metadata associated with the modification(e.g., add modifications of content items of smaller size areprioritized over add modifications of content items of larger size,delete modifications of content items of larger size are prioritizedover delete modifications of content items of smaller size, etc.).

These rank rules may be stored by the system and may be designed toachieve various performance goals for content synchronization. Forexample, delete modifications may be prioritized over add modificationsin order to free as much of potentially limited storage space for a userbefore new content items may be added. Adding of smaller content itemsmay be prioritized over larger content items in order to provide as muchprogress with respect to the number of content items added as soon aspossible.

At operation 835, the system may provide the set of operations to thecontent management system and/or the client device. As noted above,modifications associated with actions performed by the contentmanagement system may not be reflected at the client device.Accordingly, in this scenario, the system may generate a client set ofoperations configured to operate on the content items stored on theclient device to converge the server state and the file system state andthis client set of operations may be provided to the client device forexecution at operation 835.

On the other hand, modifications associated with actions performed bythe client device may not be reflected at the content management system.Accordingly, in this scenario, the system may generate a server set ofoperations configured to operate on the content items stored by thecontent management system to converge the server state and the filesystem state and this server set of operations may be provided to thecontent management system for execution at operation 835.

In some cases, both cases may be true and a client set of operations anda server set of operations may be generated and provided to theirintended recipients at operation 835. The set of operations may alsoinclude a number of checks to ensure tree constraints are maintained.For example, the set of operations may resolve various conflicts orconstraints as discussed with respect to FIG. 6.

Once the set(s) of operations are provided to the intended recipient(s),the method may return to operation 805 and await new modification data.For example, with respect to the scenario illustrated in FIG. 9, the setof operations may include retrieving the content item associated withnode 914 from the content management system and adding it to the localfile system of the client device. This would result in the addition of anode corresponding to node 914 in the local tree (not shown in FIG. 9)and sync tree 950. On the next iteration of process 800 of FIG. 8, theadd modifications of node 916 and node 918 represented by the “Add(6, 5,Bar)” and the “Add(7, 5, Bye)” entries in reference 982 are no longerblocked because their parent, node 914, has already been added to thesync tree. Accordingly, the add modifications of node 916 and node 918represented by the “Add(6, 5, Bar)” and the “Add(7, 5, Bye)” entries inreference 982 may be added to the unblocked list of actions and used togenerate one or more sets of operations configured to converge theserver state and the file system state.

The set(s) of operations may provide one or more steps for theincremental convergence of the server state and the file system state.Although implementing an incremental process may be more complex attimes, the incremental process may achieve a reduction in processingtime and reduction in the memory required. These and other initialtechnological improvements naturally lead to additional technologicalimprovements. For example, because processing time is reduced, thelikelihood of additional changes from the client device or the contentmanagement system making certain modifications obsolete or out of datais reduced as well.

With respect to FIG. 9, various groupings of content items,modifications, actions, or file identifiers are described as lists forthe purpose of illustration. Other types of data structures are alsocompatible. For example, the unblocked list of actions may beimplemented as a B-tree data structure in order to keep data sorted andallow searches, sequential access, insertions, and deletions inlogarithmic time.

Scheduler

In some embodiments, a client synchronization service may generate a setor sequence of operations configured to converge the server state andthe file system state and provide the operations to the contentmanagement system or client device for execution. However, in somescenarios, changes on the file system of the client device or on thecontent management system may cause the generated set of operations tobecome out of date or obsolete while the set of operations is in theprocess of executing. Various embodiments are directed to providing atechnical solution to these and other technical problems. For example,the client synchronization service may be configured to monitor changeson the file system of the client device or on the content managementsystem and update the client device and/or content management as needed.Furthermore, the client synchronization service may be configured toimprove performance and reduce processing times by allowing forconcurrent execution of operations.

According to some embodiments, planner 225 of client synchronizationservice 156 shown in FIG. 2 may generate a plan or plan of operationsthat consists of an unordered set of operations. All operations within aplan have no dependencies and, as a result, are able to be executedconcurrently in separate threads or in any order. The operations in theplan, according to some embodiments, are abstract instructions that maybe taken by the content management system and/or the client device inorder to converge the states and tree data structures. Exampleinstructions may include a remote or local add of a content item, aremote or local delete of a content item, a remote or local edit of acontent item, or a remote or local move of a content item.

Scheduler 230 of client synchronization service 156 shown in FIG. 2 maybe configured to receive the plan of operations from planner 225, managethe execution of the operations in the plan, determine if the plan hasbeen updated or changed, and manage the execution of the updated orchanged plan. For example, scheduler 230 may coordinate with file systeminterface 205 and server interface 210 to execute the tasks and stepsneeded to implement operations in the plan. This may include receivingconfirmations from the file system or content management system or errorhandling activities such as handling retries when there is no networkconnectivity or when a content item is locked by some other application.

Each operation may be implemented by a script or thread referred to as atask. The task coordinates the application of an associated operationand may include one or more steps needed to implement the operation. Forexample, a “local add operation” may indicate that a content item hasbeen added to the local file system of the client device and, as aresult, the content item should be added at the content managementsystem in order to sync the server state and the file system state.Accordingly, the local add operation may be associated with a “local addtask” that includes one or more steps needed to implement the local addoperation. The steps may include one or more of notifying the contentmanagement system of the new content item, uploading the content item tothe content management system in one or more blocks of data, confirmingthat all blocks of data have been received by the content managementsystem, making sure the content item is not corrupted, uploadingmetadata for the content item to the content management system, andcommitting the adding of the content item to the appropriate location atthe content management system.

A task may begin execution, suspend at well-defined points while waitingon the completion of other events, resume when the events have occurred,and eventually terminates. According to some embodiments, scheduler 230is configured to cancel, regenerate, or replace tasks. For example,based on changes to the server state or the file system state, a taskmay become stale before it is executed and scheduler 230 may cancel thestale task before it is executed.

As described above, planner 225 may generate a plan of operations basedon a set of tree data structures (e.g., a remote tree, a sync tree, anda local tree). Over time, planner 225 continues to generate plans ofoperations based on the status of the tree data structures. If the treedata structures change to reflect the state of the server state and thefile system state, planner 225 may also generates a new updated planthat differs from a previous plan. Scheduler 230 executes each plan ofoperations generated by the planner 225.

In some scenarios, changes in the operations of a subsequent plan maycause unintended behaviors conflict with an operation in the previousplan that is in the process of execution. For example, as operations ina first plan are being executed, one or more of the operations arecanceled (or are not present) in the second plan. To illustrate, FIG. 10shows an example scenario in which, at time t1, the server staterepresented by the remote tree and the file system state represented bythe local tree are synchronized as shown by the remote tree, the synctree, and the local tree all matching. Based on this synchronized state,planner 225 may generate a plan with no operations (e.g., an empty plan)at t1.

A user on the client device may delete content item A from the localfile system or move content item A out of a folder managed by clientsynchronization service 156, which is reflected by the removal of node Afrom the local tree at time t2. Planner 225 may generate a plan thatincludes operation LocalDelete(A) based on the state of the tree datastructures at time t2. Scheduler 230 may initiate the task or stepsrequired to implement the LocalDelete(A) operation. These steps mayinclude transmitting instructions to the content management system todelete content item A.

After instructions to delete content item A are transmitted to thecontent management system, the user on the client device may undo thedelete of content item A or move content item A back to the previouslocation. The local tree is updated based on this new action at time t3and planner may generate a new plan that is empty with no operations.Once again, the tree data structures match and the system is in asynchronized state at time t3.

However, because instructions to delete content item A were transmittedto the content management system, the content management system deletescontent item A from the server state. Although scheduler 230 may attemptto cancel the deletion of content item A, the instructions may havealready been transmitted and completed by the content management system.This change in the server is communicated to client synchronizationserver 156, which updates the remote tree by deleting node A at time t4.Planner 225 could notice the change in the remote tree and thedifference between the remote tree and the sync tree and determine thatcontent item A was removed at the server state. Accordingly, planner 225would create a plan with a RemoteDelete(A) operation at time t4. In aneffort to synchronize the server state and the file system state,content item A would eventually be deleted from the client device andthe local tree.

Problematically, the removal of content item A from the server state,the generation of the RemoteDelete(A) operation, and the eventualremoval of content item A from the file system state are all notintended and may cause further problems down the line for the user.Furthermore, in some cases, applications or processes may also accesscontent items and unintentional synchronization behavior may cause acascade of additional technical issues. Various embodiments are directedto preventing unintended consequences in synchronization of contentitems between a server state and a file system state.

According to some embodiments, when canceling a task for a staleoperation that is no longer in a plan of operations, scheduler 230 maywait for the cancelation to be completed before proceeding to initiatethe execution of other tasks. For example, scheduler 230 may wait toreceive confirmation of the cancelation from the client device or thecontent management system before proceeding with other tasks. Scheduler230 may determine whether the task has been initiated and if the taskhas not been initiated, scheduler may cancel the task and confirm thatthe task is no longer awaiting execution. If the task has beeninitiated, the confirmation may come from the client device or thecontent management system and notify the scheduler that all of the stepsassociated with the canceled task have been undone. According to someimplementations, scheduler 230 does not allow for cancelation of a taskonce it has been initiated. This may be the case for all tasks or acertain subset of tasks or task types (e.g., a commit task that sends anupdate on the file system state to the content management system forsynchronization with the server state).

In order to improve performance and allow for concurrent execution oftasks as well as the cancelation of tasks, scheduler 230 may also beconfigured to manage the execution and cancelation of tasks based ondifferences between a first plan of operations and an updated secondplan of operations. FIG. 11 shows an example Venn diagram 1100representation of two plans of operations, in accordance with variousembodiments of the subject technology. Planner 225 may generate a plan 11110 with a first set of operations, receive an update to the tree datastructures, and generate an updated plan 2 1120 with a second set ofoperations.

Plan 1 1110 and plan 2 1120 may share a number of common operations,which is represented by portion 1130 of the Venn diagram 1100. Plan 11110 and plan 2 1120 may also share a number of operations that are notin common. For example, operations in plan 1 1110 that are not in plan 21120 are stale and no longer current based on the update to the treestructures detected by planner 225. These stale operations of plan 11110 are represented by portion 1140 of Venn diagram 1100. Newoperations in plan 2 1120 that are not in plan 1 1110 are represented byportion 1150. Each of portions 1130, 1140, and 1150 which represent thedifferences and commonalities between plan 1 1110 and plan 2 1120 mayinclude no operations or many operations depending on the updates to theserver state and the file system state that are reflected in the treedata structures.

Because the operations in portion 1140 are no longer in the most recentplan, scheduler 230 may cancel tasks associated with these operations.In order to prevent unintended synchronization behavior, tasksassociated with operations in plan 2 that are not in plan 1 (e.g., inportion 1150) are postponed until the cancelation of tasks associatedwith operation in portion 1140 is completed. However, because operationsin each plan are configured to be able to be executed concurrently,tasks associated with operations in the intersection of plan 1 and plan2 represented by portion 1130 may be executed concurrently with thecancelation of tasks associated with operation in portion 1140 withouthaving to wait for their completion. By allowing for the concurrentcancelation of task associated with portion 1140 and the execution oftasks associated with portion 1130, more efficient use of availablecomputing resources may be achieved as well as a reduction in processingtime.

FIG. 12 shows an example method for managing changes in plans ofoperations, in accordance with various embodiments of the subjecttechnology. Although the methods and processes described herein may beshown with certain steps and operations in a particular order,additional, fewer, or alternative steps and operations performed insimilar or alternative orders, or in parallel, are within the scope ofvarious embodiments unless otherwise stated. The method 1200 may beimplemented by a system such as, for example, client synchronizationservice 156 of FIG. 2, running on a client device.

The system may be configured to receive updates from a contentmanagement system and/or the client device with regards to content itemsassociated with a content management service. For example the system mayreceive server modification data for content items stored by a contentmanagement service and update, based on the server modification data, aremote tree. The remote tree represents the server state for contentitems stored by the content management system. The system may alsoreceive client modification data for content items stored on the clientdevice and update, based on the client modification data, a local tree.The local tree represents the file system state for content items storedon the client device.

At operation 1205, the system may receive a first set of operationsconfigured to converge a server state associated with the contentmanagement system and a file system state associated with the clientdevice. For example, the system may identify differences between a synctree and a remote tree or the sync tree and a local tree and generatethe first set of operations based on any differences between the trees.The sync tree represents a known synced state between the server stateand the file system state.

The system may begin to implement the first set of operations. Forexample, in some cases, the operations are in a format ready to betransmitted to the content management system and/or the client devicefor execution. In other cases, the operations may be translated into oneor more tasks, scripts, or execution threads that may be managed by thesystem. The system may interface with the content management systemand/or the client device according to the tasks, scripts, or executionthreads in order to converge the server state and the file system state.

During this time, the system may continue to receive modification datafrom a content management system and/or the client device with regardsto content items associated with the content management service. Basedon the modification data, the system may update the remote tree or localtree and generate a second set of operations based on the updates to thetree data structures. At operation 1210, the system may receive thesecond set of operations.

At operation 1215, the system identifies a first operation in the firstset of operations that is not in the second set of operations, if any.If the system finds an operation in the first set of operations that isnot in the second set of operations, this operation may be stale and outof date as a result of changes specified in the modification data.Accordingly, the system will initiate the cancelation of the firstoperation at operation 1220. The cancelation of the first operation mayinclude a number of steps, a number of confirmation receipts for thesteps, and a non-trivial amount of processing time.

At operation 1225, the system identifies a second operation that isincluded in both the first set of operations and the second set ofoperations, if any. If the system finds an operation in both the firstset of operations and the second set of operations, this operation maybe still be valid notwithstanding changes specified in the modificationdata. Furthermore, since the operations in both sets of operations areconfigured to be able to be executed concurrently or in any order withrespect to other operations in the set, the second operation cancontinue execution while the first operation is canceled. Accordingly,the system will initiate the execution of the second operation atoperation 1230 without waiting for the first operation to completecancelation.

At operation 1235, the system identifies a third operation that is inthe second set of operations, but not in the first set of operations, ifany. If the system finds an operation in the second set of operationsthat is not in the first set of operations, this operation may be a newoperation as a result of changes specified in the modification data. Inorder to prevent unintended consequences, the system will initiate thewait for the completion of the cancelation of the first operation. Atoperation 1240, the system may determine that the first operation hascompleted cancelation and, as a result, initiate the execution of thethird operation at operation 1245.

Updating the Local Tree

As described above, the local tree is configured to reflect the filesystem state for content items stored on the local file system of theclient device. For example, file system interface 205 of clientsynchronization service 156 in FIG. 2 is configured to make changes tothe local file system of the client device (e.g., add, delete, move,edit, or rename one or more content items), detect changes to the localfile system, and update the local tree based on the changes to the localfile system. The changes may be caused by a user action on the filesystem, a third-party application running on the client device, or bythe client synchronization service synchronizing the file system statewith the server state.

Various embodiments of the subject technology provide various technicalsolutions to updating the local tree based on changes to the local filesystem. The local tree, along with the other tree data structures, iscrucial to the synchronization processes between the client device andthe content management system in various embodiments. For example, oncean update to the local tree is made, the rest the system reacts to theupdate and, in some cases, the changes to the local tree may besynchronized and applied to the server state at the content managementsystem. Accordingly, it is important to be careful about how the localtree is updated.

For example, if a user renames a file from A.txt to B.txt, in somecases, the system may detect a delete of content item A.txt and an addof content item B.txt. This may cause a node for A.txt to be deleted onthe local tree and a node for B.txt to be added. However, this resultsin a case where, for some time, no node for the renamed content itemexists on the local tree. This can cause significant damage to dataintegrity because the client device, the client application, and/or theclient synchronization service may be shut down, fail, or reboot beforethe node for B.txt is added and, as a result, a user's content item islost. The loss of the user's content item may then be synchronized tothe server state at the content management system. Similar risks areassociated with a user moving a content item from one location toanother.

Additionally, the changes to the local file system may be detected outof order and may include a large number of changes that are notnecessarily all related to a single action by a user or application. Theclient application may also be turned off or not running while manychanges to the local file system are made. On startup, the clientapplication may crawl the local file system, compare it with the localtree, and determine which changes to the local file system have occurredwhile the client application was off. These changes may not be in properchronological order. These factors may also result in unintendedsynchronization behavior if the local tree is not carefully updated.

A set of constraints may be used to ensure tree data structure integrityand protect against unintended synchronization behavior. The constraintsmay include, for example, that (1) all nodes in a tree are associatedwith a file identifier (fileID), (2) all nodes in a tree have a uniquefile identifier, (3) non-empty parent nodes cannot be deleted, (4)deleted nodes are actually deleted (and not merely moved) or removedfrom a location managed by the client synchronization service, (5) allsibling nodes have unique file names irrespective of case, (6) all nodesmust have an existing parent, and/or (7) all sibling nodes agree ontheir parents file id (DirFileID). In some implementations, a subset ofthe constraints above may be used, alternative or additional constraintsmay be used, or a combination. The set of constraints may be applied toall tree data structures or merely a subset of the tree data structureswhile a different set or sets of constraints may be applied to othertree data structures.

When a change to the local file system is detected, the change may bechecked against the set of constraints. If the change is consistent withthe set of constraints, the local tree can be updated based on thechange to the local file system. If the change violates one of theconstraints, the constraint may require additional conditions to besatisfied. For example, a constraint may require additional file eventsto be observed before the changes can be applied to the local tree, oneor more remediation steps to be performed, or a combination. As actionsoccur to satisfy certain constraints (e.g., remediation steps are takenor additional file events occur) other constraints may be violated.Accordingly, the set of constraints may be continually checked until allconstraints are satisfied. Once the constraints are satisfied, thechanges associated with the file events may be applied to the localtree.

FIG. 13 shows an example scenario, in accordance with variousembodiments of the subject technology. In particular, FIG. 13 shows thecurrent state of local tree 1310 when file event 1315 is detected. Forexample, the client synchronization service may compare the file systemwith local tree 1310 and discover that a content item exists in the filesystem at the path /root/a/b/c.txt but a node for a content item at/root/a/b/c.txt does not exist in local tree 1310. Accordingly, a fileevent 1315 may be generated specifying an add of a node at/root/a/b/c.txt is needed on local tree 1310.

The client synchronization service may add file event 1315 to a set ofobserved file events for update and determine whether the observed fileevent 1320 is consistent with a set of constraints and discover thatobserved file event 1320 violates one of the constraints in the set. Inthe scenario illustrated in FIG. 13, the observed file event 1320violates the “all nodes must have an existing parent” constraint. Morespecifically, the parent of the node to be added at /root/a/b/c.txt doesnot exist nor does the grandparent of the node. Accordingly, additionalfile events (the addition of the parent and grandparent node) must beobserved before the change is applied to the local tree.

The client synchronization service may detect additional file events andadd them to the set of observed file events for update. For example, theclient synchronization service may detect the add /root/a file event andthe add /root/a/b file event. Once these file events are observed, theviolated constraint is satisfied (and no other constraints areviolated). As a result, all of the observed file events for update maybe applied to the local tree. More specifically, a node may be added at/root/a, a node may be added at /root/a/b, and a node may be added at/root/a/b/c.txt. Accordingly, the client synchronization service groupstogether related file events for an atomic or unitary update. As will bedescribed in further detail, grouping together related file events foran atomic update to the local tree increases tree data structureintegrity, protects against unintended synchronization behavior, andprevents intermediate states in the local tree.

FIG. 14 shows an example method for updating a local tree, in accordancewith various embodiments of the subject technology. Although the methodsand processes described herein may be shown with certain steps andoperations in a particular order, additional, fewer, or alternativesteps and operations performed in similar or alternative orders, or inparallel, are within the scope of various embodiments unless otherwisestated. The method 1400 may be implemented by a system such as, forexample, client synchronization service 156 of FIG. 2 running on aclient device.

At operation 1405, the system detects a file event and adds the fileevent to a set of observed file events. For example, on startup, thesystem may crawl the file system of the client device, collectinformation on the file system, and compare the collected informationwith the local tree which represents the last known state of the filesystem. The system may identify differences between the local tree andthe file system of the client device and generate a number of fileevents based on the identified differences. Alternatively, oradditionally, the system may monitor the file system during runtime,detect changes made to the file system that are not reflected in thelocal tree, and generate file events based on the detected changes tothe file system. The generated file events may be thought of asobservations about the file system that are made by the system.

At operation 1410, the system will check the set of observed file eventsagainst a set of local tree constraints to determine whether any of theobserved file events violates a local tree constraint. If none of theobserved file events violate any of the constraints in the set of localtree constraints are violated, the set of observed file events may beused to update the local tree at operation 1435.

Each violation of a constraint may be associated with a remediationconfigured to satisfy the constraint. For example, a violation of the“all nodes must have an existing parent” constraint may be associatedwith a requirement that the addition of the parent node be observed, asillustrated in FIG. 13.

In other cases, a violation of a constraint may require actions to betaken to resolve the violation and satisfy the constraint. For example,when a user copies a content item in the file system and creates a newcopy of an existing content item, the new content item may have the samefile identifier as the original content item. The system may observe theaddition of the new copy, but this new copy violates the constraint that“all nodes in a tree have a unique file identifier.” The violation ofthis constraint may be associated with the remediation steps ofrequesting a new file identifier for the content item and assigning thenew content identifier to the content item, thus resolving the violationand satisfying the constraint, before the local tree is updated.Accordingly, the local tree will at no point be in a state that violatesany constraint.

In another example, a user may create a new content item in a locationof the file system where the file name already exists, albeit withdiffering letter case. To illustrate, a user may create a file named“A.txt” when the file “a.txt” already exists with the same file systempath. The operating system of the client device may allow for this whilethe client synchronization service may not. The system may observe theaddition of the new content item, but this new content item violates theconstraint that “all sibling nodes have unique file names irrespectiveof case.” The violation of this constraint may be associated with theremediation steps of editing the name of the new content item to denotethat a case conflict exists. For example, the “A.txt” file may berenamed “A(case conflict).txt,” thus resolving the violation andsatisfying the constraint. The file event may be removed and the processrestarted such that a new file event for the addition of the “A(caseconflict).txt” content item is detected or the file event for “A.txt”may be updated to reflect the new name “A(case conflict).txt.”

If one or more observed file events violate one or more constraints, thesystem may determine whether the violated constraint requiresremediation actions to be taken at operation 1415 or whether theviolated constraint requires additional file events to be observed atoperation 1425. If additional remediation actions are required, atoperation 1420, the system may execute the additional remediationactions. If additional file events are to be observed, at operation1430, the system may detect additional file events and add the fileevents to the set of observed file events at operation 1430.

The process then returns to operation 1410 to determine whether the setof observed file events violate the local tree constraints. In somecases, the execution of the remediation actions or the new file eventsadded to the set of file events may cause new violations of one or moreconstraints that must be resolved before an update to the local tree canbe performed. Accordingly, the process may iterate until no moreviolations of the local tree constraints exist. The process may thenproceed to operation 1435, where the system may update the local treebased on the observed set of file events.

Updating the Local Tree with Move or Rename Changes

According to some implementations, move or rename operations on contentitems on the local file system may introduce additional technicalproblems. For example, in some cases when content items such as files orfolders are moved from an old location to a new location by the user oran application, the operation may appear to the file system or clientapplication as a delete of the content items from the old location andan add of new content items at the new location. Similarly, a rename ofa content item from an old filename to a new file name may appear as adelete of the content item with the old filename and an add of a newcontent item with the new file name. Furthermore, if the content item isa folder that is the parent of many other content items, with apotentially deep and complex tree structure, a move or rename of thecontent item may also appear as a delete of all descendent content itemsfrom their old location or path to a new location or path.

As described above, intermediate states where content items are deletedor removed from the local tree before they are re-added in the newlocation or with the new name is undesirable and increases datavulnerability where a user's data may be lost. Additionally, move orrename operations appear as delete operations to the clientsynchronization service until a corresponding add operation is detected.However, the add operation may not be detected for a long time after thedelete operation is detected based on the size and complexity of thelocal file system. For example, the client synchronization service maycrawl one portion of the local file system and discover the delete ofthe content item and not discover that the content item has been addedto another portion of the local file system, thereby completing the moveoperation, until the client synchronization service crawls that portionof the local file system.

Various embodiments of the subject technology are directed to providingtechnical solutions to these and other technical problems by providing amore efficient and faster method of determining whether a deleteoperation is part of a move or rename operation or simply a deleteoperation.

FIG. 15 shows an example method for updating a local tree in response toa move or rename operation, in accordance with various embodiments ofthe subject technology. Although the methods and processes describedherein may be shown with certain steps and operations in a particularorder, additional, fewer, or alternative steps and operations performedin similar or alternative orders, or in parallel, are within the scopeof various embodiments unless otherwise stated. The method 1500 may beimplemented by a system such as, for example, client synchronizationservice 156 of FIG. 2 running on a client device.

At operation 1505, the system detects a delete event for a content item.The system may crawl or monitor changes to the local file system of theclient device or a portion of the local file system that the system isconfigured to manage (e.g., a content management folder). The system maycompare the local file system with the local tree in order to identifydifferences between the local file system and the local tree. The deleteevent may be detected based on one or more identified differences. Forexample, a node for a content item exists in the local tree at aparticular location but does not exist at that location on the localfile system. This may indicate that a user or application has performedan action that caused the content item to be removed from that location,which causes the system to detect the delete event.

The action that caused the delete event to be detected may be caused bya user or application moving the content item to another locationmonitored by the system, moving the content item to another location notmonitored by the system, renaming the content item (which may be treatedas a move by some file systems), or actually deleting the content item.In order to determine what user action caused the delete event and/orwhether or not an add event associated with the delete event will be orhas already been detected, the system may identify an operating systemprovided identifier for the content item at operation 1510.

In some embodiments, the operating system provided identifier may be aninode identifier and is different from the file identifier provided bythe content management system and/or client synchronization service. Inmany cases, the operating system may provide the inode identifier inorder to, among other things, allow for quick querying of the locationof a content item based on the inode identifier. For example, someoperating systems may provide an interface where the system may queryfor a current path or location of a content item using the inodeidentifier as a key. At operation 1515, the system may determine thelocation of the content item by querying the operating system for thelocation of the content item. In response to the query, the operatingsystem may return with the current location or path in the local filesystem of the content item referenced by the inode identifier.

Using the current location of the content item, the system may determinewhat action caused the delete event. For example, if the currentlocation is a null location or otherwise indicates that the content itemis no longer on the local file system, the action that caused the deleteevent is an actual delete. Accordingly, the system can appropriatelydelete the node for the content item from the local tree. If the currentlocation is a location not managed by the system (e.g., the clientsynchronization service), the action that caused the delete event islikely a move of the content item from its previous location to itscurrent location. However, because the content item is moved outside theterritory managed by the system, the system no longer needs to track thecontent item and can delete the node for the content item from the localtree.

If the current location is a new location that is still managed by thesystem, the action that caused the delete event is also a move of thecontent item from its previous location to its current location.However, because the content item is still within a territory managed bythe system, the system should await the detection of a corresponding addevent and treat the delete event and the add event together as a moveaction and update the local tree atomically, mirroring the actual actionthat caused the delete event.

Similarly, if the current location is the same location as the oldlocation, which is managed by the system, the action that caused thedelete event is also a rename of the content item from its previouslocation to its current location. In some file systems, renameoperations and move operations are related in that a rename operation istreated as a move operation from one location with one name to the samelocation with a new name. Accordingly, the system should await thedetection of a corresponding add event (with the new name) and treat thedelete event and the add event together as a move or rename action andupdate the local tree atomically, mirroring the actual action thatcaused the delete event.

Accordingly, at operation 1520, the system determines whether the deleteevent is associated with an add event for the content item based on thelocation of the content item. If the delete event is not associated withan add event, the delete event may be processed at operation 1525. Ifthe delete event is associated with an add event, the system may waitfor the add event, detect the add event for the content item atoperation 1530, and process the delete event with the add event in aunitary update to the local tree at operation 1535.

Although method 1400 of FIG. 14 and method 1500 of FIG. 15 are describedseparately, the two methods may work in conjunction with one another inorder to update the local tree. For example, if the delete event is notassociated with an add event, the delete event may be processed withoutcombining the delete event with a corresponding add event at operation1525 of FIG. 15. According to some embodiments, processing the deleteevent may include operations illustrated in FIG. 14 where, for example,the delete event may be added to a set of observed file events andchecked to determine whether a local tree constraint is violated.

For example, if the content item associated with the delete event hasone or more descendant nodes in the local tree, the “non-empty parentnodes cannot be deleted” constraint may be violated. The remediation forthis violation may include waiting to observe additional file events(e.g., delete events for every descendant node of the content item).Once the additional file events are detected and constraints for theseadditional file events may be checked, including a check to determine ifadditional delete file events are associated with additionalcorresponding add events. Once all of the observed file events arevalidated, the file events may be batched together and used to updatethe local tree.

Similarly, if the delete event is associated with an add event, thesystem may wait for the add event. Processing the delete event with theadd event in a unitary update to the local tree at operation 1535 mayinclude adding both events to the set of observed file events,determining whether they violate any local tree constraints, performingappropriate remediations if they do, and updating the local tree basedon the entire set of observed file events.

FIG. 16 shows an example of computing system 1600, which can be forexample any computing device making up client device 150, contentmanagement system 110 or any component thereof in which the componentsof the system are in communication with each other using connection1605. Connection 1605 can be a physical connection via a bus, or adirect connection into processor 1610, such as in a chipsetarchitecture. Connection 1605 can also be a virtual connection,networked connection, or logical connection.

In some embodiments computing system 1600 is a distributed system inwhich the functions described in this disclosure can be distributedwithin a datacenter, multiple datacenters, a peer network, etc. In someembodiments, one or more of the described system components representsmany such components each performing some or all of the function forwhich the component is described. In some embodiments, the componentscan be physical or virtual devices.

Example system 1600 includes at least one processing unit (CPU orprocessor) 1610 and connection 1605 that couples various systemcomponents including system memory 1615, such as read only memory (ROM)1620 and random access memory (RAM) 1625 to processor 1610. Computingsystem 1600 can include a cache of high-speed memory 1612 connecteddirectly with, in close proximity to, or integrated as part of processor1610.

Processor 1610 can include any general purpose processor and a hardwareservice or software service, such as services 1632, 1634, and 1636stored in storage device 1630, configured to control processor 1610 aswell as a special-purpose processor where software instructions areincorporated into the actual processor design. Processor 1610 mayessentially be a completely self-contained computing system, containingmultiple cores or processors, a bus, memory controller, cache, etc. Amulti-core processor may be symmetric or asymmetric.

To enable user interaction, computing system 1600 includes an inputdevice 1645, which can represent any number of input mechanisms, such asa microphone for speech, a touch-sensitive screen for gesture orgraphical input, keyboard, mouse, motion input, speech, etc. Computingsystem 1600 can also include output device 1635, which can be one ormore of a number of output mechanisms known to those of skill in theart. In some instances, multimodal systems can enable a user to providemultiple types of input/output to communicate with computing system1600. Computing system 1600 can include communications interface 1640,which can generally govern and manage the user input and system output.There is no restriction on operating on any particular hardwarearrangement and therefore the basic features here may easily besubstituted for improved hardware or firmware arrangements as they aredeveloped.

Storage device 1630 can be a non-volatile memory device and can be ahard disk or other types of computer readable media which can store datathat are accessible by a computer, such as magnetic cassettes, flashmemory cards, solid state memory devices, digital versatile disks,cartridges, random access memories (RAMs), read only memory (ROM),and/or some combination of these devices.

The storage device 1630 can include software services, servers,services, etc., that when the code that defines such software isexecuted by the processor 1610, it causes the system to perform afunction. In some embodiments, a hardware service that performs aparticular function can include the software component stored in acomputer-readable medium in connection with the necessary hardwarecomponents, such as processor 1610, connection 1605, output device 1635,etc., to carry out the function.

For clarity of explanation, in some instances the present technology maybe presented as including individual functional blocks includingfunctional blocks comprising devices, device components, steps orroutines in a method embodied in software, or combinations of hardwareand software.

Any of the steps, operations, functions, or processes described hereinmay be performed or implemented by a combination of hardware andsoftware services or services, alone or in combination with otherdevices. In some embodiments, a service can be software that resides inmemory of a client device and/or one or more servers of a contentmanagement system and perform one or more functions when a processorexecutes the software associated with the service. In some embodiments,a service is a program, or a collection of programs that carry out aspecific function. In some embodiments, a service can be considered aserver. The memory can be a non-transitory computer-readable medium.

In some embodiments the computer-readable storage devices, mediums, andmemories can include a cable or wireless signal containing a bit streamand the like. However, when mentioned, non-transitory computer-readablestorage media expressly exclude media such as energy, carrier signals,electromagnetic waves, and signals per se.

Methods according to the above-described examples can be implementedusing computer-executable instructions that are stored or otherwiseavailable from computer readable media. Such instructions can comprise,for example, instructions and data which cause or otherwise configure ageneral purpose computer, special purpose computer, or special purposeprocessing device to perform a certain function or group of functions.Portions of computer resources used can be accessible over a network.The computer executable instructions may be, for example, binaries,intermediate format instructions such as assembly language, firmware, orsource code. Examples of computer-readable media that may be used tostore instructions, information used, and/or information created duringmethods according to described examples include magnetic or opticaldisks, solid state memory devices, flash memory, USB devices providedwith non-volatile memory, networked storage devices, and so on.

Devices implementing methods according to these disclosures can comprisehardware, firmware and/or software, and can take any of a variety ofform factors. Typical examples of such form factors include servers,laptops, smart phones, small form factor personal computers, personaldigital assistants, and so on. Functionality described herein also canbe embodied in peripherals or add-in cards. Such functionality can alsobe implemented on a circuit board among different chips or differentprocesses executing in a single device, by way of further example.

The instructions, media for conveying such instructions, computingresources for executing them, and other structures for supporting suchcomputing resources are means for providing the functions described inthese disclosures.

Although a variety of examples and other information was used to explainaspects within the scope of the appended claims, no limitation of theclaims should be implied based on particular features or arrangements insuch examples, as one of ordinary skill would be able to use theseexamples to derive a wide variety of implementations. Further andalthough some subject matter may have been described in languagespecific to examples of structural features and/or method steps, it isto be understood that the subject matter defined in the appended claimsis not necessarily limited to these described features or acts. Forexample, such functionality can be distributed differently or performedin components other than those identified herein. Rather, the describedfeatures and steps are disclosed as examples of components of systemsand methods within the scope of the appended claims.

What is claimed is:
 1. A computer-implemented method comprising: detecting a delete event for a first content item at a first location on a local file system of a client device, wherein the first location on the local file system is managed by a content management system; determining that the delete event is associated with an add event for the first content item based on querying for a second location for the first content item; and based on the determining: waiting for the add event to be processed; and after the add event is processed, processing the delete event for the first content item at the first location with the add event for the first content item at the second location in a unitary update to a local tree, wherein the local tree represents a file system state.
 2. The computer-implemented method of claim 1, wherein the detecting the delete event comprises: comparing, by the content management system, the local file system with nodes of the local tree to identify the delete event.
 3. The computer-implemented method of claim 1, further comprising: detecting a second delete event for a second content item at a third location on the local file system of the client device; determining that a current location of the second content item is not managed by the content management system; and deleting a node for the second content item from the local tree.
 4. The computer-implemented method of claim 1, wherein the second location is identical to the first location and the first content item associated with the add event has a new name.
 5. The computer-implemented method of claim 1, wherein the determining that the delete event is associated with the add event comprises identifying that a first file identifier associated with the delete event matches a second file identifier associated with the add event.
 6. The computer-implemented method of claim 1, wherein the processing the delete event with the add event includes adding the delete event and the add event to a set of observed file events and updating the local tree based on the set of observed file events.
 7. The computer-implemented method of claim 1, further comprising: determining that an update action associated with the first content item violates a constraint that non-empty parent nodes cannot be deleted; and based on the determining: waiting for delete events for each descendant node of a parent node associated with the first content item to be processed; and after the delete events for each descendant node of the first content item are processed, processing the delete event for the first content item at the first location with the delete events for each descendant node of the first content item in the unitary update to the local tree.
 8. A non-transitory computer readable medium comprising instructions, the instructions, when executed by a computing system, cause the computing system to: detect a delete event for a first content item at a first location on a local file system of a client device, wherein the first location on the local file system is managed by a content management system; determine that the delete event is associated with an add event for the first content item based on querying for a second location for the first content item; and based on the determining: wait for the add event to be processed; and after the add event is processed, process the delete event for the first content item at the first location with the add event for the first content item at the second location in a unitary update to a local tree, wherein the local tree represents a file system state.
 9. The non-transitory computer readable medium of claim 8, wherein the instructions further cause the computing system to: compare, by the content management system, the local file system with nodes of the local tree to identify the delete event.
 10. The non-transitory computer readable medium of claim 8, wherein the instructions further cause the computing system to: detect a second delete event for a second content item at a third location on the local file system of the client device; determine that a current location of the second content item is not managed by the content management system; and delete a node for the second content item from the local tree.
 11. The non-transitory computer readable medium of claim 8, wherein the second location is identical to the first location and the first content item associated with the add event has a new name.
 12. The non-transitory computer readable medium of claim 8, wherein the determining that the delete event is associated with the add event comprises identifying that a first file identifier associated with the delete event matches a second file identifier associated with the add event.
 13. The non-transitory computer readable medium of claim 8, wherein the processing the delete event with the add event includes adding the delete event and the add event to a set of observed file events and updating the local tree based on the set of observed file events.
 14. The non-transitory computer readable medium of claim 8, wherein the instructions further cause the computing system to: determine that an update action associated with the first content item violates a constraint that non-empty parent nodes cannot be deleted; and based on the determining: wait for delete events for each descendant node of a parent node associated with the first content item to be processed; and after the delete events for each descendant node of the first content item are processed, process the delete event for the first content item at the first location with the delete events for each descendant node of the first content item in the unitary update to the local tree.
 15. A system comprising: one or more processors; and a non-transitory computer-readable medium storing instructions that, when executed by the one or more processors, cause the one or more processors to: detect a delete event for a first content item at a first location on a local file system of a client device, wherein the first location on the local file system is managed by a content management system; determine that the delete event is associated with an add event for the first content item based on querying for a second location for the first content item; and based on the determining: wait for the add event to be processed; and after the add event is processed, process the delete event for the first content item at the first location with the add event for the first content item at the second location in a unitary update to a local tree, wherein the local tree represents a file system state.
 16. The system of claim 15, wherein the instructions further cause the one or more processors to: compare, by the content management system, the local file system with nodes of the local tree to identify the delete event.
 17. The system of claim 15, wherein the instructions further cause the one or more processors to: detect a second delete event for a second content item at a third location on the local file system of the client device; determine that a current location of the second content item is not managed by the content management system; and delete a node for the second content item from the local tree.
 18. The system of claim 15, wherein the second location is identical to the first location and the first content item associated with the add event has a new name.
 19. The system of claim 15, wherein the determining that the delete event is associated with the add event comprises identifying that a first file identifier associated with the delete event matches a second file identifier associated with the add event.
 20. The system of claim 15, wherein the processing the delete event with the add event includes adding the delete event and the add event to a set of observed file events and updating the local tree based on the set of observed file events. 